Cook chow mein noodles according to package instructions, then drain and set aside.
Heat vegetable oil in a large pan or wok over medium-high heat.
Add minced garlic and stir-fry for about 30 seconds until fragrant.
Add sliced chicken breast and cook until golden brown and cooked through, about 5-7 minutes.
Remove chicken from the pan and set aside.
Add broccoli, bell peppers, and carrots to the pan; stir-fry for 3-4 minutes until tender-crisp.
Return the cooked chicken to the pan with the vegetables.
Add the cooked noodles, soy sauce, oyster sauce, and sesame oil; toss to combine.
Cook for an additional 2-3 minutes, ensuring everything is well coated and heated through.
Season with salt and pepper to taste, then garnish with chopped green onions before serving.