Heat a large skillet over medium heat and add the olive oil.
Add the diced onion and diced red bell pepper and sauté until the vegetables are softened, about 4–6 minutes.
While the vegetables cook, cut the chicken into bite-sized pieces and season with salt and pepper.
Add the seasoned chicken to the hot skillet and cook, stirring occasionally, until browned and cooked through, about 6–8 minutes.
In a small bowl, whisk together the cold water, hoisin sauce, soy sauce, sugar, cornstarch, Worcestershire sauce, sesame oil, minced garlic, and ground ginger until smooth.
Pour the sauce into the skillet with the chicken and vegetables along with the red dried chiles; stir to combine and simmer until the sauce thickens, about 2–3 minutes.
Stir in the sliced scallions and the salted roasted peanuts, toss to coat, then remove from heat.
Serve the Kung Pao Chicken over white rice.
