To make this Pepper Jack Rice Bake gluten free, substitute the cream of celery soup with a certified gluten-free condensed soup or a homemade gluten-free cream sauce, since many canned soups contain gluten. You should also verify that the shredded cheese, sour cream, chopped green chiles, and any frozen corn are labeled gluten free, as additives can vary by brand. The rice, vegetables, and seasonings are naturally gluten free, but if cross-contact is a concern, use clean utensils and bake the casserole in a thoroughly cleaned dish.