Place fillets in a single layer on a greased baking dish or broiler pan; brush with lemon juice. Combine Parmesan cheese, mayonnaise, salt, butter, and green onions, and hot sauce in a small bowl; set aside.
Broil flounder fillets 4 to 6 minutes, or until fish
flakes easily with a fork. Remove from oven and spread with cheese mixture.
Broil about 30 seconds longer, or until cheese is lightly browned and bubbly. Garnish with sliced lemon and parsley if desired.
Broiled flounder recipe serves 6 to 8.