To make this Pizza Sauce gluten free, use certified gluten-free tomato paste, Parmesan cheese, dried herbs, spices, and seasonings. Check the labels on the red pepper flakes, cayenne pepper, and grated Parmesan, as some packaged ingredients may be processed in facilities with gluten. Serve the sauce with gluten-free pizza dough, gluten-free flatbread, or gluten-free breadsticks. The sauce itself can be gluten free when all packaged ingredients are verified.