In a cooking pot boil the water and add the chilies, the garlic, the onion and leave for 5 minutes in boiling water.
Remove all the boiled ingredients and liquefy. Empty them in a clean cooking pot and season with salt and pepper.
Fry the tortillas in a pan with some hot oil and reserve.
In a greased refractory, place a tortilla layer, then the chicken breasts with some sauce and a cheese layer on top. Repeat those steps until the refractory is fully completed, placing a cheese layer on the top so it gratins.
Cook in a preheated oven at 350ºF for 25 minutes or until it gratins.