In a medium bowl, combine the olives, tomatoes, thyme, oregano, oil, capers, and lemon juice.
Spray a grill rack with nonstick, nonflammable cooking spray. Preheat the grill to medium-high heat.
Sprinkle the fish with salt and pepper. Grill the tuna until desired degree of doneness, about 3 minutes per side. Serve the tapenade over the grilled fish.