Wash and pat dry the chicken; and cut into one-inch cubes.
Add soy sauce, garlic paste and ginger paste. Mix well; cover and refrigerate the chicken for at least half an hour or overnight for better results.
Add cornstarch, salt, black pepper and an egg to the marinated chicken. Mix well until all chicken pieces are coated well.
In a large saucepan, heat oil over medium-high heat. Add chicken pieces to the oil one at a time. Cook chicken for 8 - 10 minutes or until golden brown and no pink juice running through when cut.
Carefully remove chicken from the oil with a slotted spoon and drain it on a paper towel to remove the excess oil.
Prepare the sauce by whisking together the ketchup, chili sauce, hoisin sauce and tomato paste.