To make this recipe gluten free, use a certified gluten-free pasta that holds up well in cold pasta salads, such as a corn-and-rice blend or chickpea-based pasta. Also confirm that the pesto sauce, mozzarella balls, and any packaged ingredients are certified gluten free or free from cross-contact concerns, as some brands may contain additives. Rinse the pasta carefully after cooking and avoid overcooking, since gluten-free pasta can become softer more quickly in cold salads. If preparing the salad in a shared kitchen, use clean cookware, utensils, and prep surfaces to help prevent gluten contamination.