Preheat the oven broiler or grill to high. Place whole red bell peppers on a rimmed baking sheet lined with foil. Broil or grill, turning every 3–4 minutes with tongs, until skins are blackened and blistered all over (about 10–15 minutes).

Transfer the hot peppers to a bowl and cover tightly with plastic wrap or place in a sealed paper bag for 10–15 minutes to steam — this loosens the skins.

Once cool enough to handle, remove stem, seeds and peel the blackened skin. Slice the roasted peppers into 1/2-inch strips and set aside.

Cook aromatics

Heat 2 tablespoons extra-virgin olive oil in a large skillet over medium heat. Add the finely chopped yellow onion and a pinch of salt; cook until translucent and just beginning to brown, about 6–8 minutes. Add the minced garlic and cook 30–45 seconds until fragrant.

Add the sliced roasted peppers to the skillet, stirring to combine. Cook 3–4 minutes to warm through and let flavors meld.

Stir in the halved olives, rinsed capers, sherry vinegar, chopped oregano, sugar (if using), 3/4 tsp salt and 1/2 tsp freshly ground black pepper. Cook another 2 minutes to blend. Taste and adjust seasoning (add a touch more vinegar or sugar if needed). Remove from heat and keep warm.

Tuna Steaks

Pat the tuna steaks dry with paper towels. Season both sides evenly with 1.5 tsp kosher salt and 1 tsp freshly ground black pepper.

Heat 2 tablespoons olive oil in a heavy skillet or cast-iron pan over high heat until shimmering but not smoking (about 1–2 minutes).

Add the tuna steaks to the hot pan and sear without moving: for rare center, sear 1.5–2 minutes per side; for medium-rare, 3 minutes per side. (Tuna cooks quickly — internal temp ~115–125°F rare, 125–135°F medium-rare.)

Remove tuna to a plate and let rest 2 minutes; do not slice yet.

To Serve & Garnish

Slice the tuna steaks across the grain into 1/2-inch slices. Spoon a generous portion of the warm pepperonata onto a serving platter or individual plates.

Arrange the sliced tuna on top of or alongside the pepperonata. Drizzle with the remaining 1 teaspoon extra-virgin olive oil and scatter chopped parsley over the dish.

Serve with lemon wedges so diners can squeeze fresh lemon over the tuna. Adjust final seasoning with salt and pepper to taste.