Plunge tomatoes in boiling water for 30 seconds. Dip at once into cold water. Peel skin from tomatoes. Slice stem end from tomaotes. With sharp knife3, make 3 or 4 vertical cuts in top of tomato, cutting about halfway through tomato. Place, cut side up in an 8 inch square baking dish. Pour 1/4 inch of water in bottom of dish.
Preheat broiler. Mix blue cheese salad dressing and onion. Spoon a heaping tablespoon of mixture over each tomato. Broil about 4 minutes or til bubbly and lightly browned. Top with crumbled bacon and parsley. Makes 4 servings.