1. Cook noodles: Boil the noodles in water until they're al dente. Drain and set aside.
2. Cook chicken: Heat oil in a pan and cook the chicken until it's browned and cooked through.
3. Sauté vegetables: Add the diced onion, carrot, and capsicum to the pan and sauté until tender.
4. Combine chicken and vegetables: Add the cooked chicken back into the pan with the vegetables.
5. Add noodles and season: Add the cooked noodles to the pan and stir-fry for 2-3 minutes. Add soy sauce or stir-fry sauce (if using) and season with salt and pepper to taste.
6. Serve: Serve hot and enjoy!