For the beef, whisk together the soy sauce, rice vinegar, brown sugar, sesame oil, ginger and garlic until the sugar is mostly dissolved. Place the sliced beef in a shallow dish (like a 9X13-inch pan) and pour the marinade over, tossing to coat well. Cover and refrigerate for at least 4 hours or up to 24 hours.

When ready to cook, heat the oil in a cast iron or nonstick skillet over medium heat until hot and rippling. Dump in the steak and marinade and cook, turning the beef, until sizzling and cooked through. If you want the beef more caramelized, only add half the steak at a time and cook in a single layer and then repeat with remaining beef. Remove the steak from the pan to a plate or dish and simmer any remaining sauce in the pan until caramelized and slightly thickened. Pour the sauce over the beef.

For the slaw, in a large bowl, combine the cabbage, carrots, cucumbers, and cilantro. In a small bowl whisk together the lime juice, soy sauce, olive oil, salt and pepper (start with a pinch of each and add more to taste, if needed), and sriracha. Pour the dressing over the slaw and toss to combine. Refrigerate until ready to serve (it can be made 4-6 hours in advance).

For the sauce, stir together all the ingredients and refrigerate until ready to serve (it can be made several days in advance).

For serving, place cooked steak in tortillas and top with slaw, sauce, avocado slices (optional), and serve with fresh lime wedges (also optional).