To make this recipe gluten free, replace the all-purpose flour in the coating with a gluten-free all-purpose flour blend and confirm that the cornstarch and baking powder are labeled gluten free. Use gluten-free soy sauce or tamari in both the marinade and the sauce, and check the chili garlic sauce, ketchup, tomato purée, and stock carefully, as some brands may contain gluten or be processed with gluten-containing ingredients. If you are cooking for someone with celiac disease or a strong gluten intolerance, make sure your frying oil, utensils, bowls, and cookware are free from cross-contact as well.