Start by ensuring the chicken is dry. Pat it with a paper towel to remove excess moisture. Mix soy sauce, ginger-garlic paste, salt, and red chili powder (if using) in a bowl. Add the egg white and toss the chicken pieces to coat them thoroughly. Next, add the corn starch and flour. Stir everything well, and set it aside for at least 1 hour for maximum flavor infusion.
Heat oil in a deep pan on medium-high heat. Once the oil is hot, test it by dropping a small bit of batter into the oil. If it rises without browning instantly, the oil is ready. Fry the chicken pieces in batches, making sure they don’t stick together. Turn occasionally to ensure even cooking. Once golden and crispy, drain the pieces on a paper towel.
Use just a touch of the leftover oil in a pan. Sauté garlic and ginger until fragrant, then add onions and sauté again until translucent. Add the capsicum and stir-fry for 2 minutes before pouring in soy sauce, red chili sauce, ketchup, and vinegar. Finally, add the cornstarch dissolved in water/stock, and cook until the sauce thickens and bubbles.
Add the fried chicken into the sauce and toss well, making sure all the pieces are coated. Top it off with chopped spring onions. Serve immediately!