In a medium bowl whisk together the sauce/marinade: 2 tablespoons cornstarch, 1/2 cup rice vinegar, 1/2 cup reduced-sodium soy sauce, 1/4 cup sugar, and 1/4 teaspoon pepper until the cornstarch and sugar are fully dissolved.

Place the 1 pound chicken (cut into bite-size pieces) in a large freezer bag, add 1/4 cup of the prepared marinade to the bag, seal, and toss to coat the chicken. Refrigerate the bag and marinate the chicken for 30 minutes up to overnight. Reserve the remaining marinade in the refrigerator.

Bring a large pot of generously salted water to a boil and cook 8 oz vermicelli or thin spaghetti until al dente according to package directions. Drain and set the noodles aside (toss briefly with a little sesame oil if you want to prevent sticking).

While the pasta cooks, dry-roast 1 cup peanuts in a large wok or skillet over medium heat, tossing occasionally, until golden, about 3 minutes. Remove the peanuts from the pan and set aside.

When ready to cook, heat sesame oil in a large nonstick skillet or wok over high heat. Add the marinated chicken (let excess marinade drip off) and cook, stirring occasionally, until the chicken is cooked through and lightly browned, about 3–5 minutes. Remove the cooked chicken to a plate.

Reduce heat to medium. If the pan looks dry, add more sesame oil. Add 2–4 teaspoons red pepper flakes or 8–12 dried red chilies (deseeded and halved), 5 minced garlic cloves, and 1 tablespoon freshly grated ginger. Sauté about 30 seconds, until fragrant.

Add the drained 18 oz can sliced water chestnuts, 2 chopped celery stalks, 1 chopped red bell pepper, and 2 cups snow peas (trimmed and halved). Sauté the vegetables about 1 minute, until crisp-tender.

Return the cooked chicken to the pan. Whisk the reserved sauce (it may have settled) and pour it into the skillet. Bring to a boil, then simmer until the sauce thickens and coats the chicken and vegetables, about 30 seconds.

Stir in the roasted peanuts, 5 chopped green onions, and the cooked noodles. Toss everything together and cook 1–2 minutes more, until heated through and well combined.

Taste and adjust seasoning with salt, pepper, or extra red pepper flakes as desired. Serve immediately.