Tuna with Roasted Cipolline Onions

2 pounds cipolline onions

2/3 cup balsamic vinegar

1 tablespoon plus 1/3 cup extra-virgin olive oil

1 teaspoon salt, plus more for seasoning

1/4 teaspoon freshly ground black pepper, plus more for seasoning

3 tablespoons fresh lemon juice

2 teaspoons chopped fresh thyme leaves

6 (6-ounce) tuna steaks (about 1-inch thick)

 

Bring a large pot of water to boil. Add the onions and cook for 2 minutes. Drain and cool. Peel the onions and cut off the root ends.

Preheat the oven to 450 degrees F.

 

Toss the onions, vinegar, 1 tablespoon oil, 1/2 teaspoon of salt and 1/4 teaspoon of pepper in a 13 by 9-inch baking dish. Roast in the oven until the onions are tender and golden, stirring occasionally, about 1 hour.

 

Meanwhile, whisk the 1/3 cup oil, lemon juice, thyme, and remaining 1/2 teaspoon of salt and 1/4 teaspoon of pepper in another 13 by 9 by 2-inch baking dish. Place the tuna steaks in the marinade and turn to coat. Let stand for 5 minutes on each side.

 

Oil the grill rack and prepare the barbecue for medium-high heat. Grill the steaks to desired doneness, about 3 minutes per side for medium. Cut the steaks in half. Transfer the steaks to a platter. Spoon the onion mixture around and serve.