if you wanna go by Texmex standards, beans are basically mandatory

If you wanna go by traditional Mexican standards for what a burrito is, there really aren't any. Some parts of Mexico will tell you eggs and potato are necessary. Some will tell you it has to have serrano peppers. Central/southern Mexico will tell you that tacos and burritos are the same thing, or that burrito is just a northern way of saying "taco de harina" (flour tacos).

the vegan Texmex places around here will typically do a lot more effort than just a random assemblage of vegetables in a tortilla