1Preheat oven to 350 degrees and grease a 9 x 12 casserole dish.
2Crunch up bag of Doritos and pour into the bottom of the greased pan.
3Cook hamburger and onion; drain.
4Add taco seasoning and water and cook according to package directions.
5Pour hamburger over chips; sprinkle with cheddar cheese.
6In a large saucepan, combine the tomato soup, cream of mushroom soup and Rotel. Cook until boiling.
7Pour soup mixture over cheese and bake 20-30 minutes until the soup bubbles.
8Let stand for 5-10 minutes before serving.