Bring a large pot of salted water to a boil. Cook the whole wheat egg noodles according to package instructions until al dente. Drain and set aside.
In a small bowl, whisk together soy sauce, oyster sauce, rice vinegar, honey, grated ginger, and crushed red pepper flakes. Set the sauce mixture aside.
Heat olive oil in a large skillet or wok over medium-high heat. Add the minced garlic and sliced onion, sauté for 2 minutes until fragrant and softened.
Add the thinly sliced beef sirloin to the skillet. Cook for 4-5 minutes, stirring occasionally, until the beef is browned and cooked through.
Add the red bell pepper, broccoli florets, and snap peas to the skillet. Stir-fry for 4-5 minutes until the vegetables are tender-crisp.
Pour the prepared sauce over the beef and vegetables. Stir well to coat everything evenly and cook for an additional 2 minutes to heat through.
Add the cooked noodles to the skillet. Toss everything together gently to combine and heat the noodles through.
Remove from heat. Garnish with sliced green onions and toasted sesame seeds before serving.