Preheat oven to 375°F. Separate the scallops and sprinkle with 1 tsp salt. Fry mushrooms, green pepper, celery and onion in oil for about 10 min. (until they’re partly cooked). Make white sauce by cooking 1/4 cup butter with flour and milk. Stir constantly until sauce thickens. Remove from heat and add scallops and vegetables. Combine thoroughly in a greased 1.5L casserole dish. Melt remaining 1/4 cup butter and mix with breadcrumbs. Sprinkle cheese and crumbs over top of scallop mixture and bake for 45 min., or until casserole is bubbly around the edges and the breadcrumbs are lightly toasted.