How to tenderize large squid?
Papaya is a known tenderizer for octopus, squid, and other meats. Another option is papaya enzyme tablets found in the supplement section of drugstore. Either can be added to the recipe while marinating or cooking. The tablets have the advantage of imparting no flavor. I can't judge the amount without a recipe, but pretty hard to go wrong. Also squid and octopus must be flash grilled or cooked for a long time. Anything in between results in tough meat.