Zihuatanejo and surrounding areas
I can mention a few restaurants in Zihuatanejo. But, to tell the truth, "small, hole in the wall places" whether in town or out of dawn usually don't have very good food. In Zihua you should try La Casa Vieja, a very good restaurant and if the grilled quail is still on the menu, order it. There's also Kau-Kan--very good food with outdoor dining and a stunning view of the ocean and town. There is a good, very cheap, hole-in-the-wall restaurant downtown on the main drag where we ate lunch twice. Can't remember its name but it had something to do with Pancho Villa and the restaurant was filled with Pancho Villa photographs and memorabilia. (I just Googled and it may be La Hacienda de Pancho Villa on Benito Juarez [across from Bancomer] . . . or not, my wife's trip notes, unfortunately, often don't include the names of the restaurants where we ate, just what we ate.)
And if you want to "stay far away from tourist spots," why are you going to Zihuatanejo/Ixtapa?
my experience in other parts of Mexico has illustrated that some of the best regional food is not found in the fancy places but rather in the small, family run restaurants. Although i have not been to Zihua before, i would be surprised if this is not the case there too.
My understanding is also that Zihua is one of the least touristy places of all the major vacation areas in Mexico. Again, this might be wrong, but everything i have read about this place seems to indicate that.