In a medium bowl, add peppercorns, garlic, brown sugar, cornstarch and 1 teaspoon salt and stir to combine.
Add sliced steak and toss to coat.
In a large cast-iron skillet, over medium-high, heat the oil.
Add steak and cook, stirring frequently, until some of the edges are lightly browned; 3 to 4 minutes.
Add soy sauce and toss beef to coat; about 1 minute.
Using a slotted spoon, transfer beef to a bowl or plate.
Add cabbage to skillet, spread in an even layer and let cook, undisturbed, for 1 minute so that some pieces caramelize in the pan.
Toss and cook cabbage, stirring occasionally, until crisp-tender, 4 to 6 minutes.
Stir in vinegar and season with salt.
Add steak and any juices back to the skillet, and stir until well combined with the cabbage and warmed through; about 1 minute.
Top with toasted sesame seeds and scallions; serve with rice.