While there is no universal recipe for Mexican casserole, most of its common ingredients are naturally gluten-free. The ingredients that might contain gluten can easily be replaced with a gluten-free variety.
The main ingredients in Mexican casserole are ground beef, various vegetables, beans, spices, cheese and sour cream, all of which are naturally gluten-free. Some variations of the recipe call for corn tortillas or tortilla chips, which may contain gluten, depending on their ingredients and the environment in which they were produced.
If there is a chance the product contains gluten, it is indicated on the packaging. Gluten-free tortilla chips can be purchased in many supermarkets, health-food stores or online.