any advice ?

It's my first crop season and I'm running into a few problems with my outdoor plants . am I under/over watering ? I'm from NorCal and it gets pretty hot some days would the heat be the reason ?

Possibly over watering but you need to feed the damn thing. Lol
Way to represent nor cal with that fine specimen. Lol

That looks like either legit undernuting, especially of N, Mg, and P, or it could be overwatering, like TWS said.

Your leaves are pale but not overly droopy.

Thank you for your responses . what would be best to give them ? Any particular brands I should try ? Should I check the pH ?

You can pick up a quart of Alaska Fish Ferilizer, organic or otherwise, fairly cheaply. Apply that every couple of days until the plants green up. Only get into ph if the fish fertilizer or other Nitrogen fertilizer fails to green up the plants.