Ingredients

• 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)

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Instructions

1. 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.
2. Preheat the oven to 450 degrees F.
3. 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.
4. 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.
5. 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.