I have had luck with vegetarians at May Street Market - they have a wider vegetarian selection than most places. Not sure about vegan.
FYI, I was calling around for reservations for four earlier this week. Green Zebra was booked except for the 5:00 pm and 9:30 pm slots. May Street was able to squeeze us in at 6:30 pm when I asked nicely - but we had to cancel that reservation yesterday.
IMO, Indian Garden has very good food, but the service can be horrible. Sometimes laughably bad (waving my hands around trying to get the waiters attention when the room is 3/4 empty, 30-45 minute waits for food, etc). India House on Grand also has good Indian food, and its a much nicer place for a meal (decor, service, etc) although I find it a little overpriced.