Heat oven to 350ºF. Spray 8-inch glass baking dish with nonstick cooking spray.
In large skillet, heat oil over medium-high heat. Sauté onions 2 minutes or until crisp-tender. Add red bell pepper, chiles, chicken, sour cream and 1 ½ cup of the cheese. Cook and stir 1 minute; remove from heat.
Place crushed chips in sprayed pan. Top with chicken mixture, enchilada sauce and remaining ½ cup cheese. Bake 20 minutes or until mixture is hot and cheese is melted. Serve with toppings, if desired