I grew up in NDG, which included regular visits to Villa du Souvlaki when it was too warm to cook. Villa du Souvlaki is an inexpensive Greek restaurant located right by Vendome metro. The order is done at a counter, where your food is brought to your table. Villa du Souvlaki offers lots of seating and air conditioning during the summer months.
Villa offers limited vegetarian options including the vegetarian "souvlaki", Greek salad, dolmades, spanakopita and round French fries. I've never had fries like there's anywhere else. It's one of the reasons I keep coming back.
The food is cooked take-out style, meaning everything's cooked very quickly and served in paper plates. If you're looking for inexpensive, quick, fresh Greek food, then you must visit Villa du Souvlaki.