Brush fillets evenly with olive oil; sprinkle evenly with salt and pepper. Place fillets on grill rack coated with cooking spray; grill 3 to 4 minutes on each side or until fish flakes easily when tested with a fork.
While fish cooks, prepare Tartar Sauce. Spread about 2 1/2 tablespoons Tartar Sauce over cut sides of each bun; place 1 lettuce leaf on bottom half of each bun. Top lettuce with fish; top with remaining bun halves.