Prepare the Chicken: In a bowl, mix the chicken pieces with cornstarch, all-purpose flour, ginger-garlic paste, salt, and black pepper until the chicken is well coated. Heat a generous amount of neutral oil in a deep pan over medium-high heat. Cook the chicken pieces in small batches, frying until they are golden brown and crispy, which should take approximately 4 to 5 minutes for each batch. Drain the fried chicken on paper towels and set aside.

Prepare the Stir-Fry: In a separate large pan or wok, heat 3 tablespoons of cooking oil over medium heat. Add the chopped garlic and green chilies, sautéing for about 1 minute until fragrant. Add the cubed onions and bell peppers, stir-frying for 2-3 minutes until the vegetables begin to soften but remain crisp.

Make the Sauce: Stir in the dark soy sauce, sweet chili sauce, red chili paste, tomato ketchup, rice vinegar, salt, and black pepper. Cook for 1-2 minutes until the sauces blend well with the vegetables. In a small bowl, dissolve 2 tablespoons of cornstarch in 1 cup of water. Pour the cornstarch mixture into the pan, stirring continuously until the sauce thickens, about 2-3 minutes.

Add Mango and Chicken: Once the sauce has thickened, gently fold in the cubed mangoes and the fried chicken. Cook for an additional 2-3 minutes, allowing the chicken to absorb the sauce and the mango to warm up but not turn mushy.

Serve: Remove from heat and transfer the Mango Chicken Stir-Fry to a serving dish. Garnish with chopped spring onion greens. Serve hot with steamed rice or noodles.