Preheat oven to 400. In large skillet, cook mushrooms, onion, garlic and bouillon in margarine until tender. Remove from heat; stir in crumbs and pimiento.
Cut a slit along underside of each shrimp; do not cut through. Remove vein; brush entire shrimp with margarine. Mound stuffing mixture in hollow of each shrimp.
Place in greased shallow baking dish. Bake 10-12 minutes or until hot. Garnish with parsley if desired. Refrigerate leftovers.
Microwave Instructions: In 1 quart glass measure, microwave margarine on HIGH for 45 seconds or until melted. Add mushrooms, onion, garlic and bouillon. Microwave on HIGH for 3 minutes or until onion is tender. Stir in crumbs and pimiento. Prepare shrimp as above. Place in 2 greased 12x7 shallow baking dishes or 1 (12 ) round glass platter. Microwave on HIGH for 3 minutes or until hot. Proceed as above.