Spray a baking dish about 9x13 with cooking spray, and set aside. Preheat the oven to 400F and a large skillet to medium-high heat with a drizzle of oil.
When the skillet is hot, add the peppers and onions with the cumin, chili powder, and a sprinkle of salt. Cook, stirring, for about 5 minutes until the veggies are soft and browned at the edges. Stir in the canned chiles and turn off the heat.
Build the enchiladas. Fill each flour tortilla with about half a cup of the pepper mixture and a few tablespoons of the grated cheese. Roll up the enchiladas and place them tightly seam side down in the baking dish.
Make the sauce. Preheat another skillet to medium-high heat with a drizzle of oil. Add the mushrooms and cook, stirring, for about 7 minutes until the mushrooms are wilted and browned. Add the garlic and a sprinkle of salt. Stir for one minute, then turn off the heat. Add the sour cream and heavy cream and taste the sauce; add more salt until it is very flavorful. Pour the sauce over the enchiladas.
Top the dish with any extra cheese you have and bake for 20 minutes until hot and bubbly. Serve with any toppings you like. Enjoy!