Start by cooking your vermicelli or thin spaghetti according to package instructions. Drain and set aside, making sure to toss them with a splash of sesame oil to prevent sticking.
In a medium bowl, toss the bite-sized chicken pieces with the cornstarch, salt, and pepper. Allow it to marinate while you prep the other ingredients.
In a separate bowl, whisk together the rice vinegar, reduced sodium soy sauce, sugar, and red pepper flakes (or dried chilies). Set this sauce aside for later.
In your wok or skillet, heat a tablespoon of sesame oil over medium-high heat. Add the marinated chicken and stir-fry until golden brown and cooked through, about 5-7 minutes. Remove the chicken from the pan and set aside.
In the same pan, add a bit more sesame oil if needed, then toss in the minced garlic and grated ginger. Sauté for about 30 seconds until fragrant. Next, add the chopped celery, red bell pepper, snow peas, and sliced water chestnuts. Stir-fry for about 3-4 minutes until the veggies are tender yet crisp.
Return the cooked chicken to the pan, and pour in the sauce. Toss everything together, allowing the sauce to coat the chicken and vegetables evenly. Stir in the cooked noodles and chopped green onions, mixing until well combined. Let everything heat through for an additional 2-3 minutes.
Just before serving, sprinkle in the chopped peanuts for an added crunch. Serve hot, garnished with extra green onions or red pepper flakes if desired.
