Place the cornflour in a bowl and whisk in the stock and soy sauce to a smooth consistency. Set aside.
In a large wok or frying pan, heat the olive oil and fry the chicken, garlic and half the spring onions until the chicken is just cooked through. Add the peppers and cook for a further 5 minutes, stirring, then add the sauce.
Cook for a further 5 minutes until the sauce has thickened slightly. Stir in the remaining spring onions, along with the sesame oil and sesame seeds.
Meanwhile, microwave the rice according to the instructions on the packet. Divide into bowls and serve with the chicken stir-fry.