Prep the chicken: Pat the chicken dry and slice it thinly across the grain. Toss with 1/2 teaspoon salt, black pepper, and garlic powder if using.
This seasons it and helps it brown.
Make the quick sauce: In a small bowl, stir together soy sauce (or tamari/coconut aminos), rice vinegar, sesame oil, and red pepper flakes. Set aside.
Heat the pan: Place a large skillet or wok over medium-high heat. Add 1.5 tablespoons oil and swirl to coat.
Sear the chicken: Add the chicken in a single layer.
Cook 4–6 minutes, stirring once or twice, until browned and cooked through. Transfer to a plate.
Sauté aromatics: Add the remaining oil to the pan. Add onion and cook 2 minutes until starting to soften.
Stir in garlic and ginger; cook 30 seconds until fragrant.
Add cabbage: Pile in the sliced cabbage with 1/2 teaspoon salt. Toss well. Cook 5–8 minutes, stirring often, until wilted but still crisp-tender.
Don’t overcook.
Combine and sauce: Return chicken and juices to the pan. Pour in the sauce and toss to coat. Cook 1–2 minutes to warm through and let flavors meld.
Taste and adjust salt or soy sauce as needed.
Finish and serve: Top with green onions and sesame seeds. Serve hot as-is, or with cauliflower rice if you want extra volume.