Wash and pat dry the chicken completely. Cut it into equal-sized cubes so it cooks evenly. Toss the chicken with cornstarch, flour, ginger garlic paste, salt, and pepper until well coated.
Heat oil in a pan over high heat. Fry the chicken in batches until golden and crispy. Remove and place on a plate, keeping it aside while preparing the sauce.
Heat fresh oil in a wok and add chopped garlic and green chilies. Sauté briefly until fragrant. Add onion and bell peppers, cooking until slightly tender but still crisp.
Add soy sauce, sweet chili sauce, red chili paste, ketchup, vinegar, salt, and pepper. Stir everything well so the flavors combine evenly. Mix cornstarch with water and pour it into the pan.
Once the sauce thickens, add the fried chicken and mango cubes. Toss gently so everything is coated without breaking the mango. Garnish with spring onions and serve hot.