In a bowl, mix together the egg, 1/2 tsp of salt, dash of pepper and 2 tbsps of the cornstarch (save the remaining 1/2 tbsp for later).
Add the olive oil to a skillet and heat it over medium high. While the skillet warms up, trim the chicken thighs of excess fat and cut into 1 inch pieces. Add the chicken to the egg and cornstarch mixture and stir to coat.
Once the oil in the skillet is hot, add the coated chicken and spread it into a thin layer covering the surface of the skillet. Let cook for 5 minutes without disturbing (the chicken on one side should be golden brown).
While the chicken starts to cook, prep the sauce. In a small bowl mix together: the remaining 1/2 tbsp of cornstarch, soy sauce, water, sesame oil, brown sugar, rice wine vinegar, sesame seeds, minced ginger and minced garlic. Set sauce aside for now.
After 5 minutes, carefully flip the chicken so that the other side cooks for an additional 5 minutes until golden brown, being careful to not break the chicken up too much so that the batter remains in tact on the chicken.
After the chicken has been cooked through and golden on both sides, pour the sauce over the chicken and toss to coat, breaking up the chicken pieces and letting simmer in the sauce for 3 minutes. The sauce will thicken as it simmers.
Top the chicken with diced green onion and serve with rice!