In a large saucepan cook potatoes and chopped onion, covered, in a small amount of boiling water for 12 to 15 minutes or until tender; drain. Stir in sour cream, Monterey Jack cheese, cheddar cheese
, salt, and red pepper. Stir in chopped tomatoes. Spoon into a 2-quart rectangular baking dish. Bake, uncovered, in a 350 degree F oven about 30 minutes or until heated through. Makes 10 servings.