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, crushed red pepper flakes, and chicken broth. Set the sauce mixture aside.
In another small bowl, mix cornstarch and water until smooth to create a slurry. Set aside.
Heat 1 tablespoon of 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 fully cooked and lightly browned. Remove the chicken from the skillet and set aside.
Add the remaining 1 tablespoon of vegetable oil to the skillet.
Add minced garlic and ginger, sauté for 30 seconds until fragrant.
Add carrot, red bell pepper, broccoli florets, snap peas, and half of the green onions. Stir-fry for 4-5 minutes until vegetables 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 cook for 1-2 minutes, stirring constantly, until the sauce thickens.
Add the cooked noodles to the skillet and toss everything together until noodles are evenly coated with sauce and heated through.
Remove from heat and garnish with the remaining green onions and toasted sesame seeds.
Serve immediately.