I have a sister who is veg, and i will disagree that most sf menus have enough choices for the vegatarian. Places like zuni, for example, have always had one entree and one app which are decidedly veg. Going into a restaurant with only one item on the menu (functionally) is unpleasant - even if that item is really great 
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It comes down to the sf style of short menu. I looked at zuni, and they have 5 mains, pork, fish, lamb, chicken, veg. The apps are about same ( doubling up on fish and dropping lamb). There are only 10ish things on the menu. There might be two app sized things, it is a little hard to say. But this is the style.
I have learned to just scan a menu fast and make sure there are two or three veg choices. Indian restaurants and pizza places ( high end, low end, whatever) tends to be good choices. Japanese, Californian, italian, french are a middle ground. Chinese and most Asian tend to have less, unless the menu has dedicated markings of veg items, and you still have to ask what is meant by veg. Mexicans and South American generally far less.
As a counter example, i give you flytrap (in soma), a long favorite of mine, which has three clear veg apps, and three mains if you count the impossible burger. It is a longer menu than zuni. That is the kind of menu i look for if i am dining with a veg person.
If you like beyond meat, you are in business. The number of casual places that have beyond burgers is very high.
Greens has already been mentioned. Is bar argicole in business? There has been a descendant of that group doing good veg in soma for a while.
Sorry to not be more specific, i am checking in to say this is not a vegitarian paradise, you’ll have to do some research. We have great veg, we like to eat our meat with them 
