Brown ground beef with onions and peppers in a large skillet over medium high heat.
Add beans, tomatoes, taco seasoning and water to skillet and stir to combine.
Place half of meat mixture in a greased 13x9 casserole baking dish. The layers will go as follows starting with meat on bottom: meat, cheese, tortillas, and cheese. Then repeat again: meat, cheese, tortillas, and cheese (making sure last layer is cheese. **the cheese sort of acts as a glue keeping the layers together better**.
Bake 10-15 minutes at 400 degrees until bubbly. Garnish casserole with chopped green onions.