@ambercoco1 you can eat any protein - no restrictions, though including fats which come with them is a good thing, rather than including less natural sources.
The helpful foods , though, are the most expensive elements of any meal, and for any business producing readymeals there is always the lure of reducing the costs of ingredients and production time.
I do use pressure cookers quite a bit as they seem useful for reducing cooking times - I put the carcases of chicken, duck, any leftovers into a pressure cooker, cook until the meat falls off the bones - it is surprising how much meat there is left to free up sometimes. After removing the bones there is the basis for soups and stews, curries and casseroles.