Preparation
1-preheat oven to 350*
2-saute onions for 4 minutes in skillet sprayed with nonstick spray.
3-add tomatoes, chiles, mushrooms, beans, chili powder and cumin and simmer for 10 minutes uncovered.
4-in 11.5 by 7.5 in casserole arrange 1/3 of the tortilla strips in single layer.
5-set aside a little cheese for garnish.
6-pour 1/4 of tomatoe mixture and 1/3 of cheese over strips.
7-repeat layers ending with sour cream and lasy 1/4 tomato mixture.
8-top with reserved cheese and bake for 30 minutes.