Cheesy Chili Rellenos Casserole

1 tbsp. butter or margarine
1 cup chopped onions
2 cans (4.5-oz. each) chopped green chilis, drained
1-1/2 cups each shredded cheddar cheese*, shredded Monterey Jack cheese*
3 eggs
3/4 cup sour cream*
1/4 - 1/2 tsp. crushed red pepper flakes
1 cup chopped, seeded tomato

      Heat oven to 350ºF (175ºC).  Lightly grease an 8x8- or 9x9" pan.  Melt butter in medium skillet over medium-high heat.  Add onions: cook, stir until crisp-tender.  Stir in green chilis.  Spoon chili mixture evenly into greased pan.  Sprinkle with cheeses.  In a small bowl, beat eggs lightly.  Beat in sour cream and red pepper flakes.  Spoon egg mixture evenly over cheeses.  Sprinkle with tomato.  Bake 35 - 45 minutes, until knife inserted in center comes out clean.  Makes 6 servings.
Note:*  May substitute low- or non-fat, to reduce fat and calories.