This is one of my family's favorite Creole dishes. The recipe can be made with flounder or sole fillets, but I sometimes use locally caught kingfish bass.
In a large skillet, saute the onion, green pepper, garlic and parsley in butter until tender. Stir in flour until blended. Gradually add the cream. Bring to a boil; cook and stir for 2 minutes or until thickened. Reduce heat; Stir in cheese and lemon juice; cook and stir until cheese is melted. Add crab. Cover and keep warm.
Spread mustard on both sides of fillets. Sprinkle with Creole seasoning. Place on a greased broiler pan. Broil 4-6 in. from the heat for 3-5 minutes on each side or until fish flakes easily with a fork. Top each fillet with four to five shrimp; serve over crab sauce.