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, chicken broth, and crushed red pepper flakes. Set the sauce mixture aside.
In another small bowl, mix cornstarch and water until smooth to create a slurry. Set aside.
Heat vegetable oil in a large skillet or wok over medium-high heat.
Add the sliced chicken breast to the skillet and cook for 5-6 minutes, stirring occasionally, until the chicken is cooked through and lightly browned. Remove the chicken from the skillet and set aside.
In the same skillet, add minced garlic and ginger and sauté for 30 seconds until fragrant.
Add the carrot, broccoli florets, red bell pepper, snap peas, and half of the green onions. Stir-fry the vegetables for 4-5 minutes until they are tender-crisp.
Return the cooked chicken to the skillet with the vegetables.
Pour the prepared sauce over the chicken and vegetables, stirring to combine.
Add the cornstarch slurry to the skillet and stir continuously until the sauce thickens, about 1-2 minutes.
Add the cooked noodles to the skillet and toss everything together until the noodles are evenly coated with the sauce and heated through.
Remove from heat and garnish with the remaining green onions before serving.