Cook the rice noodles according to package instructions. Drain and set aside.

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

If using, add tofu or chicken to the skillet and cook until heated through.

Add the cooked noodles to the skillet along with soy sauce, sriracha, and rice vinegar. Toss everything together and cook for an additional 2-3 minutes.

Garnish with green onions and sesame seeds before serving.