Work first on the salsa: start by heating up a pot of water and clean the serrano peppers (remove the seeds if too much heat).
Add the dried guajillo peppers to the pot, along with tomatoes, onion, and garlic cloves. Bring these ingredients to a boil.
In the meantime, cook the ground beef in a pan with a bit of olive oil and chopped garlic. Remove the excess fat and water released by cooking in order to have the leanest meat possible.
Once the tomatoes start shedding their skin, the salsa ingredients are ready. Pour them into a food processor and blend. Add this blend to a pan with a squirt of olive oil and salt and pepper; simmer for a few minutes then set aside.
In a medium bowl, beat eggs then soak the hard corn tortillas in them.
Assemble the chilasagna! Start by pouring salsa to serve as the base. Then place one soft tortilla on the bottom and start adding the fillings in layers: beef, salsa, mozzarella cheese, then another tortilla layer. Continue layering the fillings and tortillas, ending with a final tortilla layer on top. Cover it with sauce and more mozzarella.
Bake for 10 to 15 minutes.
Remove from the oven and add the finishing touches: sprinkle Cotija cheese and cilantro on top and add a couple of slices of avocado on the side.