01 - Whisk together soy sauce, sesame oil, rice vinegar, sweetener, red pepper flakes if using, and water in a small bowl. Set aside.
02 - Heat 1 tablespoon oil in a large skillet or wok over medium-high heat. Add ground beef and cook, breaking it up with a spatula, until browned and cooked through, about 5 minutes. Drain excess fat if needed.
03 - Push beef to one side of the pan. Add remaining oil, then add onion, garlic, and ginger. Sauté for 1 minute until fragrant.
04 - Add cabbage to the skillet. Stir everything together and cook for 4 to 5 minutes, stirring occasionally, until cabbage is just tender but still vibrant.
05 - Pour in the prepared sauce. Toss well to combine and cook for another 2 to 3 minutes, allowing flavors to meld and liquid to reduce slightly.
06 - Season with salt and pepper to taste. Serve hot, garnished with sliced green onions.