Prep the chicken and beans: Pat the chicken dry and season with 1/2 teaspoon salt and black pepper.
Trim the green beans. Stir together honey, soy sauce, rice vinegar, sesame oil, and red pepper flakes (if using) in a small bowl and set aside.
Sear the chicken: Heat 1 tablespoon oil in a large skillet over medium-high heat. Add chicken in a single layer and cook, undisturbed, for 2–3 minutes to get color.
Stir and cook another 3–4 minutes until mostly cooked through. Transfer to a plate, leaving any juices in the pan.
Sauté the green beans: Add remaining 1 tablespoon oil to the skillet. Add green beans and 1/2 teaspoon salt.
Cook, stirring occasionally, for 4–5 minutes until bright green and crisp-tender. If they’re browning too fast, splash in 1–2 tablespoons water to steam.
Add aromatics: Push beans to the edges of the skillet. Add garlic and ginger to the center.
Cook 30–45 seconds, stirring, until fragrant but not browned.
Combine and sauce: Return chicken and any juices to the skillet. Pour in the honey-soy mixture. Toss everything to coat.
Bring to a gentle simmer over medium heat for 2–3 minutes.
Thicken (optional): If you want a glossy, clingy sauce, stir in the cornstarch slurry. Simmer 1–2 minutes until thickened to your liking. Taste and adjust seasoning with a pinch of salt or more vinegar for brightness.
Serve: Garnish with sesame seeds and green onions.
Serve hot over rice or noodles, spooning extra sauce over the top.