The day before if possible! Boil water, cook chicken for 20 minutes on low. Remove. Shred. Whisk marinade and add it to the chicken in a glass bowl. Stir well and let marinade for at least 30 minutes, but overnight is best.
Preheat oven to 350 degrees. In a 9x13 baking dish, pour about ½ C. of sauce to coat the bottom of the pan. Layer tortillas, shredded chicken, cheese, and sauce. Save a handful of cheese to sprinkle on top. After you have a few layers, top with cheese. Bake in the oven for 30 minutes until hot and the cheese is browned. Serve with diced avocado and diced tomato.