I sense in your question that you are tired of being offered the same dal, paneer, and potatoes when you think of having a vegetarian in a restaurant. Well, I live in Delhi, and despite it being famous for its mouth-watering street food, the local restaurants here actually have the same bring and usual stuff to offer to the vegetarians.
If you go to some fine dining places, however, you would find some which serve you a variety of vegetarian delicacies. And these are so good, that you would be forced to visit these restaurants, again and again, forgetting your KFCs and other non-veg eating points entirely.
My favorite 5 are enlisted below.
1. Sarvana Bhawan, Janpath

(Courtesy: tripadvisor.in)
It serves one of the best South Indian food in the whole of Delhi. With at least 4-5 varieties of chutney with every kind of dosa you order, you will have the feel of authentic South Indian cuisine. It serves delicious desserts and filter coffee as well.
2. Haldiram’s, Connaught Place
(Courtesy: travelingspoon.com)
Haldiram’s is one place which can never disappoint you in terms of quantity and quality. It serves you everything –from chaat to snacks to a variety of main course dishes that will make it your permanent dining place.
3. Sita Ram Diwan Chand, Paharganj
(Courtesy: lbb.in)
Want to have a delicious breakfast in Delhi? Paharganj’s this Chole-Bhathure wala should be the first thing that comes to your mind. Complement your breakfast with a glass of Lassi, and you are set for the day.
4. Sagar Ratna
(Courtesy: maps.mapmyindia.com)
Another restaurant which is known for serving authentic and delicious South Indian food and is the favourite of many Delhiites since ages. They serve the special spring dosa too, and I just love it. I can visit a Sagar Ratna anytime, any day.
5. Burma Burma, Saket
(Courtesy: madhulikaliddle.com)
The best place in Delhi to try Burmese cuisine. Khao Suey, Mandalay Laphet Thoke (Tea Leaf Salad), Tayat ti Thoke (Raw Mango Salad), Mandalay Meesha, Sticky Rice with Mushroom, Oh No Tamarind (Drink), Bubble Tea, and Matcha Ice Cream are a must-try here.