Ingredients

• 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)

Instructions

1. 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.
2. For burgers: 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.
3. 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.
4. 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.