in a large bowl, mix together, cream of chicken, cream of mushroom, rotel tomatos, and mushrooms
get out ur casserole dish and then just start layering all the ingredients, starting with the doritos so they will soften while baking, add doritos, then the mixture in ur bowl, then chicken, then the cheese, and do this over and over again til u fill up ur casserole dish. i usually make 2 pans of this cause it gets eaten up so fast
distribute evenly. and then bake @ 375 for 45 minutes to an hour. good luck.