In A Saucepan, Saute Onion And Garlic In Oil Until Tender. Add Tomatoes And Basil. Bring To A Boil. Reduce Heat; Simmer, Uncovered, For 5 Minutes. Meanwhile, Broil Fish 4-6 In. From The Heat For 5-6 Minutes. Top Each Fillet With Tomato Mixture And Cheese. Broil 5-7 Minutes Longer Or Until Fish Flakes Easily With A Fork.