Thaw fish, if frozen. Pile briquettes into a pyramid in the center of your grill, then light. After heating, arrange the coals evenly in a single layer. Test for medium-hot coals, using a 3-second count.
Meanwhile, for basting sauce, in a small mixing bowl combine Italian salad dressing, dry red wine, sliced green onion, lemon juice, and catsup; let stand for 10 minutes.
Rinse fish and pat dry with paper towels. Brush inside of each fish with a little sauce. Using a slotted spoon, remove onion from sauce and spread evenly inside fish.
Place fish in a well-greased wire grill basket. Grill, uncovered, directly over medium-hot coals for 4 minutes. Brush fish with boasting sauce.
Turn the grill basket. Grill for 3 to 5 minutes more or until fish flakes easily with a fork, brushing occasionally with basting sauce.
Transfer fish to a warm serving platter; garnish with green onion tops and lemon wedges, if desired. Makes 4 servings.