In a small bowl, combine soy sauce, tomato ketchup, vinegar, red chilli sauce (if using), cornstarch, sugar, black pepper powder, and salt. Mix well to make the sauce and then set the sauce aside.

Heat oil in a wok or large skillet over high heat. Once the oil is hot, add minced garlic and grated ginger, and stir-fry for a few seconds until fragrant. Following this, add sliced onions, bell peppers, and green chillies, and stir-fry for 2-3 minutes until the vegetables are slightly softened.

Push the vegetables to one side of the wok, and add the chicken strips to the other side. Stir-fry the chicken on high heat until it turns white and is almost cooked through. Subsequently, mix the chicken with the vegetables and continue to cook for another 2-3 minutes, or until the chicken is fully cooked.

Give the prepared sauce a quick stir and pour it over the chicken and vegetables.Stir everything together to coat the chicken and vegetables evenly with the sauce and then cook for an additional 1-2 minutes, allowing the sauce to thicken slightly.

Remove from heat and garnish with chopped spring onions. Serve the flavourful Chicken Chilli hot, accompanied by steamed rice or noodles for a complete Chinese-inspired meal.

Adjust the spice levels by adding more or less red chilli sauce according to your preference. You can also add other vegetables like carrots or mushrooms for additional texture and flavour.