Saute onion in butter. Add to bread cubes with seasoning, water, and 1/2 of the cheese. if too dry, add more water. Pack stuffing firmly inside and in front of fish. Dredge all over with seasoned flour. Bake with 3/4 cup of hot water in bottom of pan until browned and tender, about 50 minutes at 350f, basting frequently. While fish bakes cream 4 tbsp butter with 1/4 cup flour, add juice of 1 lemon or 3 tbsp juice (bottled), 3 tbsp sugar, and 1 1/2 c water. Cook over low heat, stirring until thickened. Add to gravy in pan with remaining cheese. Baste fish again with thickened gravy.