I agree with you: we Spaniards eat too much for lunch. If you are looking for a healthy "menu del dia" go to this Spanish small chain. They offer a salad buffet, a vegetable soup and a fruit juice as it personal "menu de día". I always order the whole-grain Vitabanana, which gives me energy for the rest of the day.
There are different locations in Madrid. Image: lacomilona.com
Phone number: +34 915 218 616