Preheat broiler or prepare outdoor grill, and lightly coat broiler or grill rack with cooking spray.
In a shallow glass dish, combine the vinaigrette, lemon juice, and garlic. Add halibut steaks and turn to coat. Cover and marinate in refrigerator 15 minutes.
Grill or broil fish 4 to 6 inches from heat, turning once, about 7 minutes total, or until lightly translucent; cut fish in center to test for doneness.