I'm not sure if this is exactly in the area - but we had lunch at En Diagonal Bar right on Diagonal. We found it on Trip Advisor, and I'm glad we did because we would have walked right by it- super small and not much to look at it. We were the only ones there at first. But then some locals came in, we watched the dad go with his buggy to the market and get some supplies, the mom does the cooking (I assume they were married, seemed so). It was simple stuff but yummy! And the owners were so friendly - if we had attempted more spanish I'm sure we could have talked more with them.
I was in the middle of telling a story to my friend so when my chorizo sandwich came out, I didn't start eating it. A bit later her calamari came (everything kind of came out whenever she finished making it) - and she was super distressed that I hadn't started eating my sandwich yet! I didn't know exactly what she was saying, and some other guy who had come in, maybe her kid, came over and told me she wanted me to eat it because it was meant to eat hot! So my friend and I both started shoving the sandwich in our mouths! It was super hysterical!!
Anyway, it is a really fun local experience and they were so nice!! :)
https://www.facebook.com/EnDiagonalBar
Kim