Turkish people, especially those who live and work in Istanbul, love to eat meat. It can be difficult for a vegetarian to stay well fed in a city like Istanbul, unless you are dedicated enough to stop by the grocery store and start preparing your own meals using paper plates and the coffee maker in your hotel room. Even grocery stores can be hard to find in the more touristy parts of the city. Additionally, even the notion of vegetarianism is very new to the Turkish way of thinking and many people will simply not understand the concept. If you speak enough of the local lingo to ask for food without meat they will most likely offer you chicken or fish as a replacement.
While not veggie myself, I do have many friends who are, and in respect to their plight I hope this guide to what and where in Sirkeci to eat may help you to stay fed and happy without consuming animals: (top picture is a goat cheese salad at Red River Pub)
Pilav & Kurufasulye: (rice & beans) served everywhere from 5 star to street cart. (Please note, some pilavs are cooked with chicken bullion, and some fasulyes are boiled with meat. just be careful and observe before ordering.) This picture is at Borsa Lokanta.
Simit: Sesame ring-breads sold everywhere at every time on the street of Istanbul. Just 1 lira each!
There is lots of delicious food to discover and enjoy in Istanbul, even if you are a vegetarian. This map shows some of the best places in Sirkeci to find veggie option meals:
View vegetarian in Sirkeci, Istanbul in a larger map