Preheat a large skillet or wok over medium-high heat. Prepare ingredients by slicing vegetables, mincing garlic, and grating ginger.
Season the chicken with salt and pepper. Sear in hot oil for 3-4 minutes on each side until golden brown. Remove and set aside.
Sauté onions, garlic, and ginger in the same pan for 1-2 minutes until aromatic.
Add carrots, bell peppers, broccoli, and snap peas. Stir-fry for 3-4 minutes until crisp-tender.
Meanwhile, cook the egg noodles according to package instructions. Drain and set aside.
Push vegetables to one side and scramble the beaten eggs in the empty space.
Return chicken to the pan, add noodles, soy sauce, oyster sauce, rice vinegar, and sesame oil. Toss to coat.
Garnish with scallions and sesame seeds. Serve hot.