Whenever I go home, I always have to have a helping of bistec. Whether my mother makes a pan along with rice and beans and tostones, or I go to my favorite spot for a sandwich, I must have it. I'm coming into my own right upholding our Puerto Rican roots, so I hope this makes my mother and abuela proud.
A note concerning Adobo and Sazon: These are brands of dry seasoning found in most supermarkets. You could make them at home, but the work is already done for you. I haven't had it any other way. Also, Sazon has MSG so you may omit and use achiote oil for color. It may need more salt if you go this way. —global guppie
Mix together the vinegar, oil, Sazon, Adobo, and garlic. Pour in a marinading dish and toss the onions with the marinade.
Ask your butcher to tenderize or pound your steak to about 1/4 inch thick. I have included top round because that's what I found recently most similar to the cut my family traditionally uses. If you have a Latino market, they'll probably have "bistec de bolo" which we use.
Add the steak to the onions and marinate in the fridge for at least 4 hours for the top round. You may marinate for up to 12 hours.
In a large skillet with a lid, add the steak, garlic, marinade, and half the onions (reserve the rest). Add olives plus 1 tbsp olive juice, and water. Bring to a simmer, and cover.
Simmer the steak for 30 minutes before adding the rest of the onions from the marinade as well as the other onion half. Cook for another 30 - 45 minutes until the steak is fork-tender and onions are well cooked.