Pour the dressing into a resealable plastic bag, then add the steak. Seal the bag, pressing it gently to remove excess air, then marinate at room temperature for 20 minutes (you can also refrigerate for up to a half day).
Preheat the oven to 220°C (450°F). Remove the steak from the marinade and use paper towels to pat it dry. Season with coarse sea salt on both sides. Place a lightly oiled skillet over medium-high heat. Sear the steak for 2 minutes on each side, then transfer to the oven for 7 to 8 minutes, or until the steak is cooked to medium-rare (make sure to wrap the skillet handle with aluminum foil if it is made of plastic). Transfer the steak to a clean plate or a cutting board, cover loosely with aluminum foil, and let rest for 10 minutes.
While the steak rests, prepare individual bowls with the garnishes—black beans, shredded medium cheddar cheese, avocado, bell pepper, salsa, sour cream, and green onion.
Thinly slice the rested steak across the grain and transfer to a serving plate. Warm up the tortillas in the microwave or in a skillet. Serve the steak, tortillas, and garnishes family style.