Heat skillet over medium high heat and add avocado oil. Add onions, tomatoes, bell pepper and sauté until onions are translucent. Add jalapeno rounds (optional) garlic, salt, pepper and cumin. Sauté for a few minutes until fragrant.
Add tomato sauce and cook down for 2-3 minutes. Add chicken broth and bring to a boil
Preheat oven to 400 degrees.
Add corn starch slurry while mixing and allow this to simmer for 2-3 minutes to reduce. Remove from heat and set aside. *Remove jalapeno rounds (if using) and blend if smooth sauce is preferred* In separate skillet over medium heat. Heat oil and place tortillas in one by one, quickly flip with tongs. The goal is to quickly coat with hot oil to make sure they are pliable.
To assemble, place sauce at the bottom of the dish. Then place tortillas, shredded chicken, sauce, cheese and repeat. Top with cheese and bake for approximately 15-20 minutes until the cheese is melted and sauce is bubbling. Garnish with queso fresco/cotjia, onion, cilantro, and sour cream.