Heat the olive oil in a large, deep skillet over medium-high, then add the onion, green bell pepper, red bell pepper, and jalapeno. Saute until the veggies are tender, about 10 minutes.
Add the garlic, cumin, oregano, salt, and pepper and cook until fragrant, about 30 seconds.
Add the tomato sauce, chicken stock, and jalapeno hot sauce, then stir to combine. Let the sauce simmer for 12 minutes.
To assemble the casserole, spread a thin layer of the sauce on the bottom of the prepared baking dish. Arrange 6 tortillas on top to cover the sauce, overlapping as needed.
Top with 1/3 of the chicken and 1/2 cup of cheese.
Spread 1/3 of the remaining sauce over the top, then repeat the process twice more.
Finish by sprinkling the last 1/2 cup of the cheese over the top then cover the pan with foil.
Bake for 35 minutes. Remove the foil, return the pan to the oven, then bake for 10 additional minutes, until the casserole is hot and bubbly and the cheese is melted. Let rest 5 minutes. Serve hot with desired toppings.
TO STORE: Chicken tortilla casserole leftovers may be kept in the refrigerator for up to 4 days when stored in an airtight container.
TO FREEZE: Leftover casserole (either individual portions or a whole frozen casserole) can be frozen for up to 3 months. Wrap airtight and make sure your container/pan is freezer safe. Let thaw overnight in the refrigerator.
TO REHEAT: Let the casserole come to room temperature before putting it in the oven. Then warm in a 350-degree F oven until heated through.