- 1 cup pitted Kalamata olives (about 5 ounces)
- 3 tablespoons extra-virgin olive oil
- 2 tablespoons chopped shallot
- 2 tablespoons chopped fresh mint
- 2 teaspoons chopped fresh thyme
- 2 teaspoons fresh lemon juice
- 2 pounds chilled fresh tuna steaks, finely diced
- 2 tablespoons chopped drained capers
- 2 tablespoons chopped shallot
- 1 tablespoon Dijon mustard
- 1 teaspoon minced fresh thyme
- 1 teaspoon freshly ground black pepper
- 3/4 teaspoon coarse kosher salt
- Nonstick vegetable oil spray
- 12 4-inch squares herb focaccia, or six 4-inch squares pain rustique, halved horizontally, lightly grilled
- 1 large heirloom tomato, cut into 6 slices
- 6 thin slices red onion
- 2 cups baby arugula (about 3 ounces)
- Blend all ingredients in mini processor to coarse puree. Season tapenade to taste with salt and pepper. Transfer to small bowl. DO AHEAD: Can be made 3 days ahead. Cover and chill.
- Gently mix diced tuna and next 6 ingredients in large bowl. Using moistened hands, shape tuna mixture into six 3/4-inch-thick patties (each about 4 inches in diameter). Place burgers on plate. Cover and refrigerate at least 1 hour and up to 1 day.
- Spray grill rack with nonstick spray. Prepare barbecue (medium-high heat). Grill burgers until almost cooked through, about 4 minutes per side. Arrange 6 focaccia squares or bottoms of pain rustique on work surface; spread with tapenade. Top each with burger, tomato slice, onion slice, and arugula, then focaccia or bread top. Cut burgers in half and serve.