Place the chicken in a bowl and sprinkle on the cornflour, salt, and pepper. Toss together to thoroughly coat.
Heat the oil in a large frying pan (skillet) over a medium-high heat.
Add the chicken to the pan and cook for 8-12 minutes, turning a few times during cooking, until golden brown and cooked through.
Turn the heat down to medium and add the garlic and ginger.
Fry for a further 30 seconds, moving everything round in the pan, using a spoon or spatula, constantly.
Pour in the sauce and turn the heat back up to medium-high. Cook for 2-3 minutes, stirring often, until the chicken is coated, and the sauce thickens.
Turn off the heat, remove the chicken from the pan, roughly slice and place back in the sauce, stir to coat (slicing is optional – but I like it for that 'food hall style').
Serve over rice, topped with spring onions and sesame seeds.