I just realized my current favorite "go to" lunch is vegetarian: soup/half sandwich combo of southwestern corn chowder and half a hummus wrap at SF Soup Company. They have multiple vegetarian options and everything is marked (so you don't have to ask if the soup has an animal stock base). I think my favorite falafel wrap is still Oasis Grill on Drumm (plus, they have the *nicest* people there who remember me even when I haven't been in for months).
re: Ruth Lafler
Ditto what Ruth said about Oasis Grill. Tasty food, inexpensive, friendly service. And she is right, they always remember me too. They do catering and my office is a block away so when we have a strict budget, Oasis always comes through with something that is substantial enough for everyone but not too pricey.
2114 Center St, Berkeley, CA 94704
re: Ruth Lafler
So I'm a bit late, but still maybe useful to the OP. Maybe too far north, but YoYo does a pretty tasty array of noodle dishes, most of them veg/vegan. Super cheap, too. I also occasionally enjoy a veg burrito at the San Buena taco truck that parks on that same block. And of course there's always Mixt if you don't mind the wait or mediocre ingredients. Hit up Naked Lunch (probably way too far north) if you want an amazing veg sandwich.
318 Pacific Ave, San Francisco, CA 94111
504 Broadway, San Francisco, CA 94133
How far South of Market? It's a huge area.
Off the top of my head:
Whole Foods on 4th and Harrison has a great salad bar, Darwin Cafe has delicious salads and 1-2 veggie sandwiches every day, good salads and veggie empanadas at Epicenter Cafe, Chaat Cafe, pizza and pasta at Pazzia
Closer to Market and 2nd: the kim bop at John's snack shop are super and cheap. I always like the veggie options at Arabi in Rincon Center.
337 3rd St, San Francisco, CA 94107
320 3rd St, San Francisco, CA 94107
John's Snack and Deli
40 Battery St, San Francisco, CA 94111
101 Spear St # 222, San Francisco, CA
764 Harrison St, San Francisco, CA 94107
212 Ritch St, San Francisco, CA 94107