I'm with you on the impossible burger. It's great if you're looking for something that's not meat that looks and tastes like meat. I don't like meat. Anyway, here are a few of my faves: QS: Veggie bowl at Pecos Bill's at MK, Hollywood studios has Backlot Express (veg sandwich) and Rosie's Al American (fried green tomato sandwich) Sunshine Seasons at Epcot has several Asian based entrees, (noodles and tofu) Tangierine cafe is nearly all vegetarian, Regal Eagle at Epcot has a good jackfruit sandwich, Harambe Market at AK has some veggie bowls and other veg options.
TS: HS Mama Melrose has a yummy polenta/cauliflower dish and several veg flatbreads, Epcot's Spice Road Table is vegetarian heaven, Skipper's Canteen at MK has a tofu/noodle thing that's good and Tiffin's has some options but we prefer Nomad Lounge - DELICIOUS corn soup and bread service. There are a lot more. I've been vegetarian at WDW for 20 years and I never have a problem. At table service restaurants, ASK. Sometimes they have things that aren't on the menu. Have fun!