Preheat Broiler To 500 Degrees. Coat A Broiling Pan With Nonstick Cooking Spray. Brush Both Sides Of Fillets With Lemon Juice, And Then Sprinkle With Salt And Pepper. Place Fillets Flat Side Up On Prepared Pan. In A Small Bowl, Mix Parmesan Cheese, Butter, And Mayonnaise. Broil Fish About 4 Inches From Heat For 6 Minutes. Remove Pan From Oven, And Turn Fillets Over. Spread The Cheese Mixture Evenly Over Each Fillet. Top With Tomato Slices. Broil An Additional 4 To 6 Minutes, Or Until Fish Flakes Easily With A Fork.