Heat 1 teaspoon (5ml) of the vegetable oil in a medium frying pan over moderate heat. Add 1½ tablespoons of the sugar, stirring to combine. Add the walnuts and cook, stirring constantly, for 7 minutes or until the walnuts are nicely coated and lightly crisped; put aside.
Heat the remaining vegetable oil in a large nonstick frying pan over moderately high heat. Add the capsicum and cook for 2 minutes or until crisp-tender. Add the spring onions, garlic and ginger and cook for 2 minutes. Add the chicken and cook for 4 minutes.
Combine the stock, soya sauce, sesame oil and the remaining sugar in a small bowl. Add the cornflour and mix well. Add the mixture to the frying pan, bring to the boil, then cook for 3 minutes or until the sauce is slightly thickened and the chicken is cooked. Stir in the walnuts.