Combine pimiento, green pepper, onion, celery and crab meat. Add soup, mayonnaise and seasoning to crab mixture. Combine crumbs and butter; mix 1/2 cup bread crumbs into crab mixture. Place in baking dish; cover with remaining crumbs. Bake at 350 degrees for 30 minutes. Remove from oven. Garnish with mushrooms; bake for 15 minutes longer. Serves 8.