Spray a 9 x 13 or other large baking pan with cooking spray.
Peel, devein and carefully butterfly 12 shrimp. Open shrimp and arrange on baking sheet or pan.
Melt ¼ cup butter in sauce pan and sauté 1 onion, ½ green pepper and ½ cup celery until tender.
In medium bowl, combine 1 pound crab meat, ¾ cup bread crumbs, 1 Tablespoon mustard, 4 teaspoon Worcestershire sauce, ¼ teaspoon cayenne pepper and 1 egg. Stir in the sautéed vegetables.
Top each shrimp with a good Tablespoon of crabmeat mixture. Sprinkle with paprika, optional crushed red pepper flakes and drizzle melted butter over shrimp.
Bake at 350F for 20 minutes. Then turn oven on Broil and cook for additional 6 minutes.
Sprinkle parsley on shrimp and serve hot with lemon wedges and cocktail sauce, if you like.