Place 1/2 cup corn starch in a large zipper top bag. Add chicken. Seal bag and shake so all pieces are coated in corn starch. Gently shake off each piece of chicken to remove excess corn starch. Set on a plate and set aside.
Mix zest, juice, vinegar, water, brown sugar, ginger, garlic, chili sauce and 2 Tablespoons corn starch in a bowl.
In a large, hot saute pan, add 1- 2 tablespoons olive oil. Add just enough pieces of chicken to cover pan. You do not want the pan overcrowded or the pieces won't brown properly.
Brown each side.
Once all sides are browned, remove from pan. Chicken might not be fully cooked, it will finish cooking in sauce.
Continue browning all chicken pieces.
When all chicken is cooked, add sauce to pan. Bring to a boil.
When starting to thicken, add chicken back to pan.
Continue cooking until sauce thickens and chicken cooks through.
Serve hot over rice and garnish with green onions and sesame seeds.
Time saving tips: Sauce can be made ahead of time. Chicken can be cooked ahead of time and then kept in the fridge until ready to use. Bring sauce to a boil. Add chicken. Cook until sauce is thickened and chicken is warmed through.