Preheat oven to 400° F.
Place fillet on cutting board and cut lengthwise to form a pocket.
Flake crab meat.
Melt butter in a large skillet. Sauté onion and celery until tender.
Add garlic and cook 2 more minutes.
Add parsley and green onions, remove from heat.
Stir in lemon juice, cayenne pepper and breadcrumbs.
Toss crabmeat with prawns or shrimp.
Stuff fillet pockets with seafood mixture.
Top with Parmesan cheese, paprika and melted butter.
Bake 20 to 25 minutes.
Garnish with lemon slices and parsley.