To make this Sheet Pan Sausage and Veggies Dinner gluten-free, use certified gluten-free smoked sausage and Dijon mustard, as some packaged sausages and condiments may contain gluten-based fillers or additives. Confirm that the garlic powder, Italian seasoning, paprika, Parmesan cheese, and all packaged ingredients are gluten-free. The broccoli, bell peppers, red onion, cherry tomatoes, and olive oil are naturally gluten-free when prepared without gluten-containing additives.