Prepare smoker or oven at a temperature of 350 degrees.
Sauté the onion and jalapeños for 10 minutes. Set aside.
Mix all of the ingredients in a large mixing bowl.
Line the 9x13 pan with 6 tostadas. Pour in half of the casserole mix.
Add the final 6 tostadas on top of the mixture. Pour the remainder of the casserole mix on top and spread evenly.
Top with the grated cheese topping.
Place the casserole in the smoker for 40 minutes.
Optionally, if you are using an oven you can broil for the final 5 minutes.
Remove the casserole and allow it to cool for 15 minutes. Slice, top with sour cream if you like, and enjoy!
