In a large pan, combine salsa, chicken, mushrooms and seasoning. Turn heat to low and simmer for 10 minutes or so, until mushrooms have softened and the mixture is heated through. (If the salsa has minimal liquid, you can add some water to the mix to keep it from scorching.)
Spread a handful of tortilla chips on a microwave/oven safe plate. Spoon the salsa mixture over the chips. Sprinkle with the shredded cheese.
Melt the cheese in the microwave or under the broiler. Serve with an assortment of toppers such as sour cream, guacamole, olives, chiles, etc.