Preheat the oven to 350°.
To make the sauce, bring shallots, garlic, white wine, vegetables and chicken broth to a boil in a medium saucepan.
Dissolve the flour in skim milk, then pour slowly into the hot chicken broth, stirring constantly. Reduce the heat to medium-low and cook, stirring, until thickened. Add salt, pepper, minced jalapeño chilies, and processed cheese. Stir until the cheese is melted. Set aside.
Coat a medium saucepan with vegetable spray. Over medium heat, sauté the onion, bell peppers, and chilies until softened. Season with salt and pepper and set aside.
Spray the tortilla quarters with a butter-flavored spray on both sides and place on cookie sheets. Toast in a preheated 350° oven 8 minutes. Tortillas will not be crisp. Put half the tortillas in a 9 X 13 casserole.
Put half the chicken on top of the tortillas and season with salt, pepper, and chili powder. Top with half the chilies and onions. Repeat the layers and pour the reserved sauce over all. Top with grated cheese and undrained diced tomatoes and green chilies.
Bake at 350° for 40 to 45 minutes or until hot.