Garlic reins supreme in this grilled tuna dinner. The tuna steaks are infused with garlic and thyme from the marinade and served with garlicky mashed Yukon Gold potatoes.
In a large resealable plastic bag, mix the 2 tablespoons oil, lemon juice, garlic and thyme. Add tuna and seal. Shake to coat all of the tuna with the mixture. Marinate for 20 minutes in the refrigerator.
While tuna is marinating, cook potatoes. Place potatoes in a medium-size pot and cover with cold, lightly salted water. Bring to a boil and simmer for 15 minutes or until tender. Drain and place in large bowl.
Heat the 4 tablespoons oil in a small skillet or saucepan. Add scallion, garlic and thyme. Cook for 1 minute. Mash potatoes and add in warm olive oil and garlic mixture. Add 1/2 teaspoon of the salt and 1/4 teaspoon of the black pepper. Continue to mash potatoes until desired consistency.
Heat a gas grill to medium-high or prepare a charcoal grill with medium-hot coals. Lightly coat grill rack with oil or nonstick cooking spray. Season the tuna steaks with remaining 1/4 teaspoon salt and 1/4 teaspoon black pepper. Grill for 4 minutes per side for medium. Serve tuna with the smashed potatoes on the side.