Madrid is sometimes even better for a city-break than Barcelona. But this is after seeing both and if your interest is not beach and sea, but night life, museums and complete relaxation.
So if you are in Madrid I would recommend you two completely different options for lunch or dinner, both tried personally and loved.
First option is Mama Inés Café, a restaurant in the gay area of Madrid, Chueca. So if you have an issue with that then don’t visit, although the customers are not gays. “El menu del dia” is almost upper class fusion molecular cuisine, compared to that in the area. You can have the chance to eat a cream soup that would be an exhalation for the senses.
Second option is Five Guys, declared the best hamburger in Madrid, on the Gran Via. And there is a reason for that. It is just a food to die for and there is always a queue even outside the fast food.