Preheat oven to 350℉ degrees. Spray 3 quart baking dish with cooking spray and set aside.
In a large skillet over medium heat melt the butter. Once melted add the onion, and bell peppers. Allow to cook for several minutes, stirring occasionally, until tender and browned.
Add in the garlic, cumin, chili powder, salt, and black pepper. Stir to coat the veggies in the seasonings.
Sprinkle the flour into the skillet. Stir to coat the veggies in the flour, will end up with a thick paste. Cook briefly for 2-3 minutes.
Pour in the broth and stir. Bring mixture to a boil while stirring and let simmer while stirring for about 2-3 minutes until thick. Remove from heat, allow to cool for about 2 minutes and stir in the diced tomatoes with green chiles and the sour cream. Stir to combine. Add the shredded chicken and stir until mixed. Set aside.
Pour the canola oil into a large skillet and heat over medium heat. Once the oil is heated carefully lay the tortillas in the oil in batches, cooking until just browned on each side. Remove from oil and place onto a plate lined with paper towels to catch the remaining oil.
Once all tortillas are browned layer 6 tortillas on the bottom of the baking dish. Layer the tortillas to cover as much of the dish as possible. Top with half of the chicken mixture then one third of the cheese. Repeat by layering 6 more tortillas, the remaining half of the chicken mixture, and one third of the cheese. Top with the remaining tortillas and the rest of the cheese.
Cover the baking dish with foil and bake for 15 minutes. Remove the foil and continue baking for an additional 10 minutes. Remove from the oven allow to cool for several minutes then serve warm. Can serve with additional sour cream and fresh cilantro.