To make sure this Hash Brown Egg Casserole is safe, for those following a gluten-free diet please take a moment to check the labels on the hash brown patties and any processed ingredients like ham. It's important to ensure that they don't contain any additives that may contain gluten. Thankfully most grocery stores offer gluten-free options for hash patties so you can easily find them. Additionally, it's an idea to verify that the brand of ground mustard you choose is certified gluten-free. Some varieties might include gluten as a filler ingredient. By taking these precautions you can enjoy this breakfast casserole without any concerns, about gluten. Bon appétit!