Cut up the chicken thighs and place in a large bowl. Add 1 tbsp of sesame oil, the sugar, five spice, 1 tbsp of soy sauce and 1 egg to the bowl and mix in.
Add the cornflour - plus a pinch of salt and pepper - and rub it into the chicken. This gets messy - the chicken will become gloopy and start to stick together, but make sure each piece is coated and they should separate. Add a little more cornflour if necessary.
Mix the ingredients for the sesame sauce together in a small bowl.
Prep the veg that needs prepped and set aside.
Add vegetable oil to a wok or large pot over medium high - it'll depend on the size of wok/pot you are using, but we want to shallow fry the chicken, so as much oil as that takes, please.
Add the marinaded chicken to the oil and fry until golden brown - around 6-8 minutes. Remove the chicken with a slotted spoon or slice and place on kitchen towels/over a wire rack.
In a separate pan or pot, heat 1 tbsp of sesame oil over a high heat until smoking. Add the onion and pepper and stir fry until lightly browned, then pour over the sauce and bring to a boil. Once boiling, add the chicken pieces and sesame seeds, and stir through to mix. Add salt and pepper and serve immediately.