In a bowl, combine, sugar, vinegar, ketchup, pineapple juice, oyster, and corn starch. Mix it well and set aside.
Heat 1 tablespoon of oil in a pan, saute onion until softened. Now, toss in red bell pepper. Mix it again.
Then, add the fried chicken into the pan. Mix and slowly pour the sauce. Continue stirring for 5 minutes.
After 5 minutes, transfer onto a serving plate. Sprinkle with sesame seeds.
Serve hot and enjoy!