Garlic Tuna Steaks (How to Grill Tuna Well Done)

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These amazing garlic butter tuna steaks are tender, full of flavor and perfect when served on a ciabatta roll with your favorite simple salad and a pile of fries. This recipe is my interpretation of a famous tuna prego from a wildly popular restaurant in Lisbon and showcases How to Grill Tuna Steaks Well Done.

grilled tuna steak sandwich cut open with lemon wedges and jar of yellow mustard

Creating a highly flavorful but simple marinade of butter, scallions and garlic, then grilling the tuna in foil packets so the fish gently cooks in the buttery marinade, gives you the best well done tuna experience without leaving our seafood dry and tough!

This recipe is based on one of my favorite sandwiches in Lisbon - the Tuna Prego at Sea Me in Time Out Market. It's ridiculously delicious and served simply on a brown bun with packets of yellow deli mustard.

If you're as obsessed with grilled seafood like I am, try my Foolproof BBQ Salmon and Grilled Shrimp Skewers.

Ingredients needed for this recipe:

Ingredients for recipe laid out on a counter and labeled

Before we get to the step by step directions, a few notes about the ingredients.

Fresh tuna steak: Ahi tuna is easiest to find and most economical. Most steaks are already cut around 1 inch to 1 ½ inches thick. For this recipe, I recommend buying two thicker steaks and cutting them in half lengthwise, creating four thinner tuna steak sandwiches with this recipe.
Garlic, scallions, red onion: substitute shallots for scallions in the butter, if necessary, and substitute any slicing onion for the balsamic red onions.
Deli mustard: bright yellow mustard is ideal here. I've tried it with all sorts of fancy Dijons and whole grain mustards. This sandwich sings best with the deli mustard you serve on a hot dog.

Full measurements and ingredients included in the printable recipe card below.

Step by step instructions:

1. Make garlic butter marinade

Melt 4 tablespoons of butter with garlic, scallions, salt and pepper in a small bowl in the microwave. Set aside to bring the marinade to room temperature.

Garlic scallion butter in a bowl with a spoon

2. Prep tuna

After cutting your fresh tuna steaks in half lengthwise, use paper towels to dry fish very well. (Each tuna steak should be ½ - ¾ inch thick.) Lay out 4 large pieces of aluminum foil and place one tuna steak in the middle of each. Cover each steak in garlic scallion mixture.

piece of fish marinated in garlic butter

Use a second piece of foil to create a foil pouch for each tuna steak. Set aside to marinate for 20 minutes.

3. Make easy balsamic onions

Melt butter in a large skillet and saute onions with a pinch of salt and pepper until softened and a little brown, about 15 minutes.

sliced red onions in olive butter in a white skillet

Add balsamic vinegar to the pan and cook an additional minute or two until the onions look glazed, but no liquid remains in the pain. Taste and adjust seasoning. Set aside.

balsamic glazed onions cooking in a white skillet

4. Grill tuna steaks

Preheat gas grill to medium-high heat (about 375-400℉). Add tuna packets and cover the grill. Grill tuna steaks for 4-6 minutes, or until your desired internal temperature. (145-150℉ for well done, 140-145℉ for medium/medium well, 130-140℉ for medium rare).

Tuna packets can also be cooked on a charcoal grill or baked in the oven at 400℉ for about 6 minutes.

5. Build sandwiches and serve

Open foil (watch for steam!) and serve grilled tuna steaks on ciabatta rolls with yellow deli mustard, arugula and balsamic red onions.

tuna steak sandwich served with arugula, mustard and balsamic onions

Plate the sandwiches with a wedged lemon for a squeeze of bright lemon juice over the tuna steak sandwich. Serve with one of my favorite Sides for Tuna Steaks.

finished recipe served on parchment on a black plate with lemon wedges

FAQ's and Serving Suggestions:

How do I know when a tuna steak is well done?

The best way to know when any fish or meat is well done is by checking its internal temperature by using a meat thermometer. Insert the thermometer into the thickest part of the tuna steak, and it should register between 145-150°F for well-done tuna.

How long does it take to grill a tuna steak to be well done?

Cooking time will vary depending on the thickness of the tuna steak and the heat of your grill. As a general guideline, you can grill a 1-inch-thick tuna steak to well done in approximately 4-5 minutes per side. Since we sliced our tuna steaks in half (lengthwise), your ½-inch to ¾-inch thick steaks should cook in about half the time - roughly 4-6 minutes total cook time (no flipping required).

How to store leftover tuna steak?

To store leftover tuna steaks, wrap and keep in the refrigerator for up to 2 days. To reheat, warm gently in a skillet with a bit of butter or olive oil until just heated through.

Tips for buying tuna steaks:

In a typical grocery store or fish market, you will find several different species of tuna steaks.

Yellowfin Tuna: also known as Ahi tuna, is a popular choice for tuna steaks. Ahi tuna steaks have a firm texture and a mild flavor, making it versatile for various cooking methods like grilling or searing. You can also plate this as raw tuna for a sushi or sashimi preparation.

Albacore Tuna: these tuna steaks are known for their light pink color and mild flavor. They have a tender texture and are often used in recipes that call for a milder-tasting fish. Albacore is often a less expensive variety of tuna.

Bigeye Tuna: bigeye tuna steaks have a deep red color and a rich flavor. They are slightly oilier than other varieties, giving them a robust taste. Bigeye tuna is well-suited for making a grilled tuna steak or a pan-seared preparation in a grill pan or cast iron skillet.

Bluefin Tuna: this type of tuna is highly prized for its exceptional flavor and buttery texture. However, due to concerns over sustainability, it may be less common to find it in grocery stores. If available, it is often the most expensive option.

When buying tuna steaks, it's important to consider their freshness and quality. Look for steaks that have a vibrant color, firm texture, and no signs of discoloration or strong odor. If possible, look for sustainably sourced tuna to support responsible fishing practices.

Garlic Tuna Steaks (How to Grill Tuna Well Done)

Ingredients needed for this recipe: