How to defrost coriander / cilantro?
Frozen supermarket coriander/cilantro is perfectly good to use whilst cooking. Very similar to adding stems for flavour. You'll never get fresh looking leaves to finish the dish from the ice blocks, but stir it in and you will get that background flavour. Delicate leaves, Basil is similar, are either fresh or they aren't. 

Don't worry too much about the look and you'll be fine. Bear in mind that you're adding water to the recipe, and put a pot plant on your windowsill for the finishing touches.