The Moveable Feast
The Moveable Feast is a vegetarian popup just next to London Bridge station, under The Shard (come out of the station at the bus stop, go left and down the escalators, then around the corner). FINALLY, a decent veggie option at London Bridge that's open daily and with reasonable hours (07:00-20:00).
There are three food companies, plus Three Wheels coffee (haven't tried the coffee, so can't vouch for it). Options will rotate throughout the time Moveable Feast occupies the space, and the current food vendors are Not Dogs, The Salad Kitchen, and Club Mexicana.
The vegan option for the hot dogs is a sausage in a wrap. Tasty, but a little awkward to eat, so I wish they would source vegan buns. Then again I'm likely to spill food on myself no matter the preparation, and cutlery is provided.
The jackfruit (seriously why doesn't Chrome's dictionary know this word) tacos from Club Mexicana are a solid vegan option, and are recommended. Proper tacos using corn tortillas. They are everything good jackfruit tacos ought to be, so I’ll be back for more.
The space is welcoming and fun, but the atmosphere doesn't call for long and chatty lunches. The vibe I got was eat and move along so other people can use the space, which is fine. Just don't plan a romantic dinner date here. I mean unless maybe I'm your date, because dating sounds like a horrible pastime and at least it would be over quickly. Plus I really enjoy awkwardness. So let me know if you want to eat some tacos and never hear from me again.