My favourite thing to eat at Epcot is a margherita pizza at Via Napoli, with added fontina cheese and olives. Just perfect pizza.
Chips n' queso at La Cava. Also the chips n' salsa.
The vegetarian sampler at Tangierine Cafe. The hummus is divine and I also love the lentil salad that comes with it. Fresh, healthy and really flavourful.
ALL THE CHEESE. I esp love the griddled greek cheese with honey and pistachios from the Greek F&N booth. Also at F&N, I'm a huge fan of the Colorado Chili with Cashew Cheese at Terra.
I loved the Empanadas de Queso at La Hacienda de San Angel - they came with rice and black beans and some sort of delectable cabbage mixture. SO GOOD. The salsas had a nice kick to them too.
For the other parks...
any veggie sandwich at Earl of Sandwich can't be beat. They are so delicious it's ridiculous.
All the veggie options at Tusker House in AK are awesome - the hummus, tabboleuh, etc.
At Sci-Fi Diner, I asked for the Smoked Turkey BLT without the bacon or turkey, add avocado. It was really, really yummy. Like a guacamole sandwich, haha.
The Lighthouse sandwich from Columbia Harbour House is one of the best QS meals on property, in my opinion - for vegetarians. It's hummus with tomato and broccoli slaw.
My all-time favourite little vegetarian bite is the Sonoma Goat Cheese Ravioli from California Grill.