In a small skillet heat margarine or butter over medium heat until melted. Add mushrooms and onion; cook over medium heat about 5 minutes or until vegetables are tender. Stir in parsley. Cool slightly.

Stir together rolled oats, milk, salt, pepper, and egg. Add ground beef and mix well. Place on waxed paper and flatten to a 12x8-inch rectangle. Spoon mushroom and onion mixture evenly onto meat. Roll up, starting with 8-inch end. Seal seam and ends by pinching together. Stir together catsup and mustard.

Arrange preheated coals around a drip pan in a covered grill. Test for medium-low heat above pan. Tear off a 24x18-inch piece of heavy foil. Fold in half to make a double thickness of foil that measures 18x12 inches. Trim to make a 12-inch square. Cut several slits in the foil square. Place foil on grill over drip pan. Place meat loaf on foil. Cover and grill for 50 to 60 minutes or until no pink remains in meat, brushing with catsup mixture during the last 5 minutes of grilling. Remove meat loaf from grill; cover with foil. Let stand 15 minutes before slicing. Makes 6 servings.

Prepare meat loaf; cover and chill up to 6 hours before grilling.