In small bowl, combine mayonnaise, green onions, and lemon pepper. Squeeze lemon over each halibut steak and season with blackening seasoning or just top with 1/4 cup of tartar sauce, spread to cover one side.
Preheat grill to medium high heat. Slightly grease grill. Place tartar encrusted halibut on grill. Grill for 10 minutes or until halibut flakes with fork. Serve with lemon wedges.