Place tuna steaks in a 12 x 8-inch dish; pour salad dressing over tuna. Cover and refrigerate 1 hour, turning once. Remove steaks from marinade; reserve marinade. Sprinkle pepper on both sides of steaks.
Grill, covered, over medium coals (425 degrees F) for 5 minutes on each side or until fish flakes easily when tested with a fork, basting occasionally with marinade.
Place on a serving plate; squeeze a lemon wedge over each steak.