Thaw scallops, if frozen. Halve large scallops. Rinse; pat dry with paper towels. Set aside. For marinade, in a saucepan heat butter or margarine and orange juice concentrate until butter is melted. Remove from heat; stir in parsley, tarragon vinegar, and mustard. Stir in scallops. Cover and chill 30 minutes to 2 hours.
Meanwhile, in a mixing bowl pour boiling water over mushrooms and green pepper. Let stand for 2 minutes; drain. Cut orange into 8 wedges, then halve each wedge.
Preheat broiler unit. Drain scallops, reserving marinade. On 8 long skewers alternately thread scallops, green pepper pieces, and mushrooms. Allow at least 1/4-inch space between pieces. Place kabobs on the unheated rack of a broiler pan.
Broil 4 inches from heat for 10 to 12 minutes or scallops are opaque, turning and brushing often with reserved marinade. Add orange wedges to skewers during the last 2 minutes of broiling. Makes 4 servings.