Prepare the chilies by slicing them vertically down the middle. For half of the chilies, use the tip of a knife to scrape out the seeds and discard. If you want it to be spicier, skip this part. If you want to reduce spiciness, remove the seeds from more of the chilies. Use gloves when handling chilies.
Heat 2 tbsp oil in a wide frying pan. Add onion and green pepper and stir fry until edges turn brown. Remove from pan and set aside.
Add 2 more tbsp of oil to the frying pan. Stir fry the beef on medium high (uncovered) until almost cooked through, about 10 minutes.
Add all the green chilies, followed by the water and sugar. Cover and let cook about 5 minutes.
Add the sauteed onion and green pepper back to the pan.
Dilute the cornstarch with a little bit of water in a cup and pour in. Cook for another 2 minutes.
Serve hot with rice and enjoy!