Bring a large pot of salted water to a boil. Add the lo mein noodles and cook according to package instructions until al dente, about 5-7 minutes.

Drain the noodles in a colander and rinse with cold water to stop the cooking process. Set aside.

In a wok or large skillet, heat sesame oil over medium-high heat. Add the bell pepper, carrots, broccoli, and snap peas. Stir-fry for about 5-7 minutes until the vegetables are tender-crisp.

Add the cooked noodles to the vegetables in the wok. Pour in the soy sauce, hoisin sauce, and rice vinegar. Toss everything together until well combined and heated through, about 2-3 minutes.

Serve immediately, garnished with chopped green onions and sesame seeds if desired.