Slice mushroom and onions and saute with butter until onions are clear and mushrooms are begin to get soft. Add garlic and saute for 1 extra minute.
Drain Rotel tomatoes and chilies and add into saute with 1 tsp chili powder.
Stir in cream of chicken soup and rotisserie chicken and heat through. Line 13x9 inch casserole dish with corn tortillas. Pour half of the filling over and top with another layer of tortillas. Finish with the rest of the filling and cheeses.