Hello there, Fernalie, and welcome to planDisney!
We're so happy to see you here and thanks for bringing your question to us. Congratulations on making the recent switch to becoming a vegetarian. My wife and daughter are both ovo-lacto vegetarians, so I'm familiar with looking for vegetarian friendly dishes while navigating the Parks.
I'm happy to report that the Disneyland Resort has really re-invented itself in terms of culinary offerings. I'm old enough to remember visiting back when classic theme park foods like hot dogs and chicken nuggets were the norm and very little else was available. It's refreshing how far they've come with accommodating special dietary needs and increasing the range of dishes on offer.
Currently, I think that the Disneyland Resort is very friendly to Guests on a Plant-based diet and we usually have no issues when my wife and daughter accompany me to the Parks. When you are there, you may use the Disneyland Mobile App to view any dining location to examine their menu for Plant-based dishes. In fact, in 2020 Disney partnered with Impossible Foods to bring more plant-based offerings to Disney Parks Guests, so you'll see plenty of dishes using Impossible Foods as a protein source. Here are some of my daughter's favorite dishes:
As you can see, there are plenty of options available. And if that wasn't enough, you'll be visiting just as the Disney California Adventure Food & Wine Festival begins! The Foodie Guide was recently posted and you'll find some plant-based dishes there as well so I'm hoping that you'll have a variety of choices from which to pick.
Fun Fact: Walt Disney originally designed Tomorrowland with the idea of an "Agrifuture," where edible plants would replace ornamental landscaping. In fact, most of the plants in Tomorrowland are edible! I wouldn't recommend picking up random plants and nibbling, though. If you want that type of an experience, I'd recommend visiting Garden Grill Restaurant at the Land Pavilion in Epcot Center!
Fernalie, I hope that you found this response helpful and reassuring. If you need anything else from us, please visit again anytime. You're always welcome at planDisney and we'd love to hear from you!
Wishing You a Great, Big, Beautiful Tomorrow!
-Al