Cook the rice noodles according to the package instructions. Drain and set aside.
In a large skillet or wok, heat the vegetable oil over medium-high heat.
Add the sliced chicken to the skillet and cook for about 5-7 minutes, or until browned and cooked through. Remove the chicken from the skillet and set aside.
In the same skillet, add the mixed vegetables, garlic, and ginger. Stir-fry for 3-4 minutes until the vegetables are tender-crisp.
Return the chicken to the skillet and add the cooked rice noodles. Pour in the soy sauce, oyster sauce, sesame oil, and red pepper flakes (if using). Toss everything together and cook for an additional 2-3 minutes until heated through.
Remove from heat and garnish with sliced green onions and sesame seeds before serving.