To tenderize the steak, poke the steak throughout with a fork or meat prongs. With a sharp knife, cut out and discard the sinew in the center of the steak. Season liberally with salt and coarsely ground black pepper. Heat 1 tablespoon of the oil in a large cast iron skillet over medium-high heat. Add the steak and sear each side, about 3 minutes per side.
To make the salsa, cut the onions into rings. Slice the chilies and garlic. Add onions to the pan with the steak, season with salt and pepper.
Add the chilies to the pan, and add a little more olive oil, if necessary. After a few minutes, add the garlic to the pan. Drizzle with the vinegar. Continue to cook the steak until it is medium-rare, 10 to 12 minutes. Rest the steak on a cutting board for about 10 minutes. Slice against the grain, season with more salt, pepper and olive oil if desired, and serve with the salsa picante.