Marinate fillets in lemon juice and lime juice for 30 minutes. Coat a piece of heavy-duty foil (about 14 in. x 14 in.) with nonstick cooking spray (or use foil pan). Pat the fillets dry with a paper towel and place on foil. Crimp foil, forming edges. Place foil flat on the grill (do not seal). Grill, close cover, over medium-hot heat for 4 minutes. Combine Parmesan cheese, butter, mayonnaise, shallots and salt; brush/spoon over fillets. Sprinkle bread crumbs on top. Grill 3-4 minutes longer or until fish flakes easily with a fork.