If you're a vegetarian, finding healthy food to eat in Madrid can sometimes be a challenge unless you know where to look. There are not as many vegetarian restaurants in Madrid as there are in, say, Barcelona. Madrid is known for its meat, fish, and seafood.
Most than any other food, Madrid is known for its ham. The jamón in Spain, as many locals will tell you, is the best in the world. There are three different kinds of ham here: Jamón Serrano, Jamón York, and Jamón Iberico. Ham is a source of pride here, and furthermore, there's a misconception among children and uneducated people that jamón is, in fact, healthy. When I taught a class of first graders about natural remedies to ward off sickness, one proud little boy announced that whenever he feels ill, he always eats a big plate of jamón with rice (arroz) and then he feels much better.
That being said, it's easy to eat healthy vegetarian food if you cook all your own meals, but there are also some good restaurants around. Below I've listed a few of my favorites.

One of the first places I discovered here was Yerba Buena. They pride themselves on gourmet cooking or "alta cocina vegetariana." This means that, in addition to being delicious, the food is arranged on the plate in a way that is aesthetically pleasing. At around €10 a meal, the food here is also surprisingly inexpensive.
Yerba Buena is located in the center of the city, near Sol, at Calle Boradores, 3. Their website is: http://www.yerbabuena.ws/. They are open from 11:00 am ― 12:00am.

Here is a map of how to get there:

Another place I love is Viva La Vida, which is a vegetarian buffet and organic market. There are two of them in Madrid and they are both open 7 days a week. Their website is: http://www.vivalavida.vg/. Below is a photo of the one near Atocha. Both have buffets. The one in Atocha (Calle Huertas, 57) is very small, so it's only for getting food to-go, although there are benches outside, and it's almost always warm and sunny in Madrid (sometimes even in the winter).

The other Viva La Vida, my favorite one, is located in La Latina. Their address is: C/ Costanilla de San Andrés, 16. That Viva Vida is much bigger, and even has a downstairs. The downstairs is outdoors-themed, with vines and wicker furniture. Here is a picture of a mural upstairs that is upstairs.

At Viva La Vida, you pay by the gram. Every gram of food costs 1,80 euros. To give you an idea of how much that is, I usually spend anywhere between 7 euros and 15 when I go there... depending on how hungry and I am and how much money I have.
There is another vegetarian restaurant that I love called Isla del Tesoro, though it's more pricey, unless you go for lunch and opt for the menú del día. Isla del Tesoro is on C/ Manuela Malasaña, 3, near Metro Bilbao. Like the other two restaurants I've mentioned, they have terrific organic food, as well as natural juices and organic beer.


However, if you're craving Indian or Bangladeshi food in particular, then the best place to go is Calle Lavapies. That street, in addition to the rest of the surrounding area, are full of Bangladeshi restaurants. The prices at these places are driven down by the fact that there's so much competition. There are even guys with menus standing in front of some of them, ready to present their best offers. (C/ Lavapies is right near Metro Lavapies, or from Metro Tirso de Molina, you can exit at C/ Magdalena, and take your first right off that street onto Lavapies.)