Preheat the oven to 400. Lightly coat 6 large scallop shells (or a shallow casserole) with non stick cooking spray. Place the crab in medium size mixing bowl and set aside.
Tear the bread into small chunks and put into food processor. Pulse to moderately coarse crumbs. Pour in melted butter and pulse to incorporate. Tip crumbs onto wax paper and put aside.
Put the parsley, salt and black and cayenne pepper into the food processor and pulse a few times until coarsely chopped. Add mayonnaise and mustard and process until smooth about 5 seconds. Blend with crab meat and toss lightly to mix.
Mound the mixture into the shells or spread thinly in the casserole and spread the bread crumbs on the top. Bake uncovered on the middle rack of the oven until bubbling and slightly brown, 12 to 15 minutes.