Step 1: In a medium bowl, combine the chicken pieces with 1 tablespoon of soy sauce, 1 teaspoon of sesame oil, and a pinch of black pepper. Toss to coat and let marinate for at least 10 minutes while you prepare other ingredients.
Step 2: While the chicken marinates, prepare your vegetables: mince garlic and ginger, slice bell pepper, carrot, and broccoli (if using). Cook noodles according to package instructions, drain, rinse with cold water, and set aside.
Step 3: In a small bowl, whisk together the remaining 3 tablespoons of soy sauce, sweet chilli sauce, peanut butter, rice vinegar, maple syrup (or honey), and sriracha (if using). Add 2-3 tablespoons of hot water to reach desired sauce consistency.
Step 4: Heat 1 tablespoon of vegetable oil in a large wok or skillet over high heat. Add the marinated chicken and cook for 3-4 minutes until browned and cooked through. Remove chicken from wok and set aside.
Step 5: Add the remaining 1 tablespoon of vegetable oil to the hot wok. Add minced garlic and ginger and stir-fry for 30 seconds until fragrant.
Step 6: Add bell peppers, carrots, and broccoli (if using) to the wok. Stir-fry for 3-5 minutes until vegetables are tender-crisp.
Step 7: Return cooked chicken to the wok. Add the drained noodles and pour the prepared sweet chilli peanut sauce over everything. Toss well to coat all ingredients evenly.
Step 8: Cook for another 1-2 minutes, stirring constantly, until the sauce has thickened slightly and everything is heated through.
Step 9: Remove from heat. Stir in sliced spring onions and half of the crushed roasted peanuts. Serve immediately, garnished with the remaining peanuts.