Add oil to the same pan. Reduce heat to medium-high.
Add chicken. Season with salt and pepper. Sauté, stirring occasionally, for 3-4 minutes or until browned.
Add egg. When egg starts to set, scramble and mix in with chicken.
Add garlic, ginger and green chilies. Sauté, stirring, for about 1 minute or until fragrant.
Add schezwan sauce and tomato sauce (ketchup). Season with salt.
Add water to cover chicken, approximately 1 cup. Stir to combine.
Bring to a boil.
Add cornflour (cornstarch) slurry. Stir to combine.
Simmer for 7-8 minutes or until chicken is cooked through.
Add more water if required.