Bistec con Cebollas

2 Tbsp vegetable oil

Season meat (both sides) with Adobo and Sazon.  Pour vinegar over meat.  Cover and refrigerate for 1 hour.  Pour oil in skillet (as always, I used cast iron) and heat to medium high heat.  Add meat and brown on each side.  While browning second side, add onion slices to skillet.