In a large zip-close plastic bag, mix together the pepper, five-spice powder, red pepper flakes, 3 tablespoons of the vinegar and soy sauce. Add the flank steak, seal the bag, then turn to coat evenly. Refrigerate for at least 30 minutes or up to 2 hours.
Meanwhile, in a small bowl, stir together the daikon radish, bell pepper, ginger, salt, the remaining 11/2 tablespoons of vinegar and the scallions. Set aside.
When you are ready to cook the steak, in a large skillet over medium-high, heat the oil. Add the steak and sear for 4 minutes per side, or until desired doneness. Allow the steak to rest on a cutting board for 8 minutes. Slice the steak thinly across the grain, then serve with the slaw. Makes 4 servings.