Mix the soy sauce, rice vinegar, and sugar together in a small bowl and set it aside. Having the sauce ready before you start cooking makes everything move faster once the beef is in the pan.

Heat the vegetable oil in a large skillet or wok over medium-high heat. Once the oil shimmers and a drop of water flicked in sizzles immediately, add the ground beef. Break it apart with a spoon and cook for 6 to 8 minutes, stirring occasionally, until it is fully browned with no pink remaining. The beef should have some caramelized bits on the bottom of the pan. That is flavor.

Push the beef to the edges of the pan to make a small open space in the center. Add the minced garlic and grated ginger to that space and cook for about 30 seconds, just until fragrant. Then stir everything together so the garlic is distributed through the beef.

Add the shredded cabbage to the pan all at once. It will look like a lot, but it wilts down quickly. Toss it with the beef and cook for 3 to 4 minutes, stirring every minute or so. You want the cabbage tender but still with a little bite. It should not be completely limp.

Pour the soy sauce mixture over everything and toss to coat. If you are using red pepper flakes, add them now. Cook for 1 more minute so the sauce soaks into the beef and cabbage.

Pull the pan off the heat and drizzle the sesame oil over the top. Stir once more. The sesame oil goes in last because high heat dulls its flavor. Taste and add a small splash more soy sauce if needed.

Serve immediately in bowls as-is for a low-carb meal, or spoon over steamed rice. Top with sliced green onions and sesame seeds.