In a deep bowl or container mix all ingredients and lay the steak cuts in the mixture. Try to completley submerge both cuts and spread the onions and pineapple evenly on top (and under if possible) the steaks. Let it sit for a day, covered to soak in all the flavoring. (the meat will start browning due to the citric acid and liquids being soaked in)
The next day just throw it on a frying pan cooking it with a little bit of the marinade (so you don't need oil or butter to grease the pan)and some of the pineapple on med to high heat until desired rarity.