Cut the chicken into 3cm cubes. Add to a bowl with the cornflour, season with salt and pepper and toss to coat the chicken evenly.
Heat the oil in a large frying pan over a medium heat. Add half of the chicken in a single layer. Cook for 4 mins on each side or until nicely browned. Transfer the cooked chicken to a plate and repeat the process with the remaining raw chicken.
Cut the red pepper into chunks and cook for 5 minutes using the same pan as the chicken. Remove and set aside.
Add the ginger and garlic to the pan and cook for 30 seconds.
In a bowl, whisk together the chicken stock, soy sauce, vinegar, ketchup, sweet chilli sauce, brown sugar and sesame oil. Add the sauce mixture to the pan.
Bring the sauce to a simmer. Mix the 2 teaspoons cornflour with 2 tablespoons cold water and mix well.
Pour the cornflour into the pan and bring to the boil. Cook for 1 minute or until the sauce has just thickened.
Add the chicken, red pepper and cashew nuts to the pan and toss to coat in the sauce.
Sprinkle with sliced spring onions and serve hot. Enjoy!