Mushrooms are awesome on pizza. I also like onions and garlic, and luckily also so does my wife! There are much better non-dairy cheese products out there (and recipes for making them yourself) than there used to be! I am impressed with some brands. Very tasty and with pleasant texture, even after cooking. Maybe you've tried some? And yes, gluten is often a huge problem. For me it's very harmful, so I haven't had any in 5 years. I had to learn to make my own pizza crusts again... out of new materials! But I now have a good recipe that works nicely. Not for tossing up to the ceiling, though, it would be a huge mess! I think gluten helps dough stretch.