On Friday I went to a long-time vegetarian restaurant called
El Estragón (web:
http://www.guiadelocio.com/estragonvegetariano ). We arrived at about 2pm and the place was nearly empty. By the time we left, 4pm, the place was FULL! I was told El Estragón has been a popular vegetarian restaurant in Madrid for many many years. It's located on
Plaza de la Paja, 10 , just "down hill" from San Andrés Church before reaching Calle de Segovia. So if you're standing at the La Latina metro station next to the large market, go WEST 3 blocks past the Cava Baja/Alta to Plaza Puerta de Moros to Plaza San Andrés, turn right, down the hill to Plaza de la Paja.
GOOD food, too. They had a Menú del Día for less than 10 Euros each. I had the spinach salad first and then a "grilled soy filet with mustard" with little cheese croquets on the side. VERY tasty - and I'm not a vegetarian restaurant fan either.
Saludos, MadridMan