DO-AHEAD TIP: Marinate fish for 15 minutes (see recipe).
Preheat grill to MEDIUM. Place fillets in a shallow dish. In a small bowl, combine next 6 ingredients (salt through lemon zest). Rub mixture into fish.
Cover and marinate for 15 minutes. Lightly oil the grill grate. Grill fillets over indirect heat for 8 to 10 minutes, turning once, until fish flakes easily when tested with a fork.
Watch carefully to prevent burning! If desired, serve fish topped with capers. Enjoy!