Prep the chicken: Pat the chicken dry and slice thinly against the grain. Toss with 1/2 tablespoon cornstarch and a pinch of salt. This helps it sear nicely without deep-frying.

Make the sauce: In a small bowl, whisk together soy sauce, water or broth, brown sugar (or substitute), rice vinegar, garlic, ginger, and red pepper flakes if using.

Mix the slurry: In another small bowl, stir 1 tablespoon cornstarch with 1 tablespoon cold water until smooth. Set aside.

Heat the pan: Place a large nonstick skillet or wok over medium-high heat. Add half the oil and swirl to coat.

Sear the chicken in batches: Add half the chicken in a single layer. Cook 2 to 3 minutes per side until lightly browned and just cooked through. Transfer to a plate. Repeat with the remaining oil and chicken.

Bloom the aromatics: Reduce heat to medium. If the pan is dry, add a splash of water. Pour in the sauce and let it bubble for 30 seconds to wake up the garlic and ginger.

Thicken the sauce: Stir the cornstarch slurry again and pour it into the pan while stirring. Simmer 30 to 60 seconds until the sauce turns glossy and slightly thick.

Combine: Return the chicken and any juices to the pan. Toss to coat. Add the scallions and cook 1 minute more to soften slightly but keep their crunch.

Finish and serve: Taste and adjust seasoning—add a splash more vinegar for brightness or a pinch more sweetener if you want it sweeter. Sprinkle sesame seeds if desired. Serve with cauliflower rice for a low-cal option or a small scoop of regular rice.