Place the oil in a large frying pan with the onion. Cook gently until the onion is translucent, about 10 minutes.
Cut the chicken into bite-sized chunks while the onion is cooking.
Add the crushed garlic and grated ginger and stir for 10 seconds, then add the curry powder and cook, stirring, for 30 seconds.
Add the chicken chunks, and stir for 2–3 minutes until lightly browned on all sides.
Mix the cornflour with a little of the stock until smooth, then add the rest of the stock and pour this mixture into the pan. Cook, stirring, until the mixture thickens a little. Simmer gently for 5 minutes, and then add the apples if using and simmer for 10 minutes more, stirring occasionally. Mix through the lemon juice and adjust seasoning.
Sprinkle with toasted coconut and serve with White Rice and some fruit chutney on the side.