Preheat the oven to 350°F and spray a 9x13-inch baking dish with nonstick cooking spray.
To a large skillet over high heat, add butter. Once the butter has melted, add onions, red pepper, and green pepper. Cook until softened (about 5-8 minutes).
Add soup, tomatoes, chicken stock, sour cream, chili powder, and cumin. Mix together until combined. Remove from heat.
Add ¼ cup of the sauce to the bottom of the prepared baking dish, spreading it out in an even layer.
Top the sauce with 12 quarter pieces of the tortillas, 1½ cups of chicken, 2 cups of the remaining sauce, and 1½ cups of cheese. Repeat with the remaining tortillas, chicken, sauce, and cheese.
Bake, uncovered, for 40 minutes, or until the cheese is bubbling.
Broil for 1-2 minutes. (To brown the cheese- this is optional.) Remove from the oven and let it rest for about 5 minutes. (It may seem runny at first, but it will set up.)
Serve garnished with parsley.