Bring a large pot of salted water to a boil.

Add the noodles to the boiling water and cook according to package instructions until al dente, about 5-7 minutes.

Once cooked, drain the noodles in a colander and rinse with cold water.

In a large skillet or wok, heat the vegetable oil over medium-high heat.

Add the sliced onions and minced garlic, cooking until the onions are translucent.

Stir in the bell peppers, carrots, and broccoli. Sauté for about 5-7 minutes until they are tender but still crisp.

Add the drained noodles to the skillet along with the soy sauce and oyster sauce. Toss everything together.

Season with salt, pepper, and sesame oil if using. Garnish with chopped green onions before serving.