Stir in the flour, ground chiles, cumin and Mexican oregano. Throw in the onions, garlic and tomato sauce. Add enough water to barely cover the mixture. Season to taste with salt and pepper. Stir the pot until the ingredients are well incorporated. Bring the liquids to a boil, cover, cut the heat to a slow simmer and braise for 1 - 1 1/2 hours. Stir the pot - on occasion. Thicken with a slurry of cornstarch and water.
Place large heaps of chili into pre-warmed tortillas, along with an amount of cheese to your liking. Fold them up burrito-style. Serve with salsa.