Place the steak in a plastic sealable bag. Add the pickled jalapeno mixture. Let marinate at room temperature for about 1 hour.
Preheat a grill or grill pan to medium high.
Brush the jalapeno mixture off the steak and discard. Season the steak with salt and pepper and grill until charred, about 3 to 4 minutes per side depending on thickness. Transfer to a cutting board and let rest.
Slice the onion crosswise 1/2 inch thick, keeping the rings together. Brush onion slices with olive oil and season with salt and pepper. Grill, turning occasionally, until soft, 10 to 15 minutes. About 8 minutes before the onion is finished, add the poblanos and jalapenos to the grill and char on all sides. Set aside until cool enough to handle, then peel off the skins, stems, and seeds. Cut the peppers into strips. (In Mexican cooking, “rajas” refers to strips of chilies.) Separate the onion rings.
Preheat a large skillet over medium heat. Thinly slice the steak on the bias, against the grain. When the skillet is hot, coat the bottom with 2 tablespoons olive oil. Add the garlic and oregano and saute about 1 minute. Add the steak, onion and pepper strips. Toss to heat through. Season with salt and pepper. Serve with tortillas, guacamole and pico de gallo.