I have made nachos this way for as long as I can remember. If there are any leftovers (rarely), I crumble them over a bed of lettuce and top with southwestern ranch dressing for lunch the next day. We eat these at least once a week.
Add taco packet plus 1/2 cup of water and stir until mixed in well.
Add can of refried beans to taco meat and add water until a good spreading consistency is reached (depends on how thick your beans are.).
In a 9x13 casserole dish, spread out half of the bag of doritos. Top with 1/2 of the meat/bean mixture and 1/2 of the cheese. Put any optional toppings on now.
Place the 2nd half of everything on top of the first layer in the same order.
Bake in a 350* oven for about 15 minutes until all the cheese is melted.