How to find a good restaurant in Spain as a tourist

My fool-proof method for finding a great mid-priced restaurant for lunch in Spain?

Go to 100 Montaditos. 

HAHA lol no do not eat there. I mean, I have eaten there many, many times in my youth, but now I cannot stomach a single montadito. I used to eat so many platters of french fries slathered in nacho cheese and beicon. What can I say, with age comes indigestion. And the wisdom to avoid that situation...most of the times. As long as it is not Euromanía...

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Anyway I digress. The real way to find a great restaurant in an unfamiliar Spanish city:

Go to the neighborhood mercado around lunch (3 pm). (NOT the food halls that look like markets but are full of tourists and only have prepared food stands. You want the neighborhood market with all the food stalls and the neighborhood people shopping with their granny carts. In Zona Alta in Barcelona, that might be a place like Mercado de San Gervasi - Mercado del Putxet, or Mercado Sarriá.)

Look for the place with the longest lines/most customers. the next day, go back at 1:30 pm* to that restaurant (in order to get a seat) and you will have one of the best meals you have ever eaten in your life.

Ensaladilla and caña, the snack of champions

Nota bene: Don't eat seafood on Mondays, it will not be fresh and the best places won't even be open on Mondays.

*1:30 is important, because nobody in Spain is thinking of lunch at 1:30. It is the equivalent of asking an american if they would like to eat lunch at 10:30 am. People will look at you weird. And yet, at 2:00 pm everything starts filling up quick and by 3 pm, olvídatelo, no encontrarás sitio en ningún restaurante--unless of course you are dining after me, because I will be vacating the table at 3 pm for a nice solitary cafelito in a now-abandoned cafetería.