Cook the whole wheat lo mein noodles according to package instructions until al dente. Drain and set aside.
In a small bowl, whisk together soy sauce, oyster sauce, hoisin sauce, rice vinegar, sesame oil, and crushed red pepper flakes. Set sauce mixture aside.
In another small bowl, mix cornstarch and cold water until smooth to create a slurry. Set aside.
Heat 1 tablespoon vegetable oil in a large wok or skillet over medium-high heat.
Add the sliced chicken breast and stir-fry for 5-6 minutes until cooked through and lightly browned. Remove chicken from wok and set aside.
Add the remaining 1 tablespoon vegetable oil to the wok. Add minced garlic and ginger, stir-fry for 30 seconds until fragrant.
Add shredded carrots, snap peas, broccoli florets, and sliced red bell pepper to the wok. Stir-fry for 4-5 minutes until vegetables are tender-crisp.
Return the cooked chicken to the wok and add the cooked noodles.
Pour the prepared sauce over the chicken, vegetables, and noodles. Toss everything together to combine evenly.
Stir in the cornstarch slurry and cook for another 1-2 minutes until the sauce thickens and coats the ingredients well.
Remove from heat and garnish with sliced green onions before serving.