Cook noodles according to package directions. Drain and set aside.
Heat oil in a large skillet over medium-high heat. Add chicken; cook until golden and cooked through. Remove and set aside.
Lower heat slightly. Add garlic and sauté until fragrant (about 30 seconds).
Stir in soy sauce, honey/brown sugar, vinegar, water/broth, and pepper. Simmer 1–2 minutes.
Add cornstarch slurry; simmer until the sauce thickens and turns glossy.
Return chicken to the pan, add noodles, and toss until evenly coated.
Finish with green onions and sesame seeds if using. Serve hot.