To make this recipe gluten free, replace the Bisquick with a certified gluten-free baking mix, and confirm that the taco seasoning, Rotel tomatoes, green chiles, mayonnaise, sour cream, and shredded cheese are all labeled gluten free or free from cross-contact concerns. Some packaged seasoning mixes and baking blends may contain hidden gluten or wheat-based thickeners, so checking labels matters here. If preparing the casserole in a shared kitchen, use clean pans, utensils, and prep surfaces to help prevent gluten contamination.