Preheat oven to 400F. Place a single layer of chips on the bottom of an oven-safe cast iron skillet. Sprinkle the cheese over the chips. Sprinkle the taco seasoning on the cheese. Spread the beans and chilis on top of the chips.
Repeat the layering process, if you would like more nachos.
Place the nachos in the oven for 5-10 minutes until the cheese is melted to your preference.
While the nachos are baking, dice up the tomato and avocado.
After removing the nachos from the oven, top with diced tomato and avocado.