Cook the Noodles: Boil noodles according to package directions until al dente. Drain and rinse under cold water. Toss with 1 tsp sesame oil to prevent sticking.
Make the Sauce: In a small bowl, whisk together soy sauce, oyster sauce, hoisin sauce, brown sugar, cornstarch, ginger, and red pepper flakes.
Cook the Shrimp: Heat vegetable oil in a wok over medium-high heat. Add shrimp and cook 2–3 minutes per side until pink and opaque. Remove and set aside.
Stir-Fry the Vegetables: In the same wok, stir-fry garlic, bell peppers, carrots, and snow peas for 2–3 minutes until tender-crisp.
Combine Everything: Add shrimp back to the wok along with the sauce. Toss well. Add noodles and stir-fry for another 2 minutes until fully coated and heated through.
Serve and Garnish: Top with green onions and optional sesame seeds. Serve hot with chili oil or soy sauce, if desired.