Combine first 5 ingredients in a food processor. Pulse 5 times or until finely chopped, scraping down sides of bowl, if necessary. Transfer to a small bowl, and set aside.
Sprinkle tuna evenly with salt and pepper.
Coat grill rack with cooking spray; place on grill over medium-hot coals (350° to 400°). Place fish on rack; grill, covered, 4 to 6 minutes on each side or until fish flakes easily when tested with a fork. Serve with tapenade. Garnish with lemon wedges and rosemary sprigs, if desired.