5 oz. package of plain Melba toast, broken into 1-inch pieces 2 T. vegetable oil 3 large egg whites 1 T. Dijon mustard 2 tsp. minced fresh thyme leaves 1/4 tsp. garlic powder 1/8 tsp. cayenne pepper 4 1-inch thick cod fillets (about 6 oz.) vegetable cooking spray salt and pepper 1 lemon, cut into wedges