To prepare a whole griddled achiote striped bass spicy pickled red onions recipe, you will first need to prepare the ingredients for the recipe. Peel the red onion and slice it in half lengthwise. Cut the onion into quarters. Scoop out the flesh from the skin of the fish and place it on the cutting board. Place the sliced onion in the refrigerator for at least 4 hours to allow the flavors to develop.