In a large bowl, combine ginger paste, garlic paste, soy sauce, and salt to make a smooth paste. Use this paste to marinate chicken for about one hour in the refrigerator.
Meanwhile, in a small bowl, combine together cornflour and water to make a thick batter. Add salt to taste. Set aside.
Heat oil in a pan. Dip the chicken pieces in corn flour batter. Shallow fry. Set aside.
Heat oil in a deep pan over medium-high heat. Add garlic and sauté for 1-2 minutes, stirring occasionally. Add onion and sauté for another 3-4 minutes, or until the onion is soft and translucent, stirring occasionally. Add the diced capsicum and sauté again for a minute, or until the capsicum is half cooked. Add soy sauce, tomato sauce, and chilly powder, and stir to combine. Reduce heat to medium-low and simmer for at least 3 minutes. Taste, season with extra salt if needed.
Serve warm, topped with chopped spring onions.