First thing, what’s the big problem with liver and onions? The onions should be ready to go, the liver should be sliced (I used to work in a place where the liver was kept in a milk bath and sliced to order, but those were different days and a different market) and your seasoned flour at hand. Where’s the problem, once you’re learned how to flip it without it splashing hot oil on the back of your hand?
If you’re looking for prep help, consider contacting an agency that helps the minimally developmentally challenged, people, for example, with mild Down’s syndrome. I used to think that this was exploitive, but a friend who worked in the field said that this was not the case, that this was, in general, the highest level of work available to these men and women. That the shame was that people who could learn and advance themselves didn’t, and stayed as prep people and dishwashers. She said that the challenged people had exemplary attendance records, and, once you taught them properly, remarkable dedication and consistent work habits.
Just a thought. If your line cook is a pain in the butt, my attitude is start looking now, quietly, and find someone else, and then beat her to the punch.