Make the marinade first.
In a medium bowl, add soy sauce, rice wine vinegar, brown sugar, sesame oil & hoisin sauce. Stir to fully mix. Set aside.
In a large bowl, add chicken and cornflour and using your hands mix to coat the chicken in the cornflour.
Heat vegetable oil in a wok on medium to high heat.
Add cashew nuts and cook until golden brown. Remove from wok and set aside.
Add more oil to the wok, if required. Add chicken & marinade and cook until chicken is browned browned (about 4-5 minutes). Stir regularly to ensure the chicken is coated with the marinade.
Add red capsicum and cook a further 2-3 minutes until capsicum softens.