Heat the oil in a non-stick wok. Chop the spring onions into short lengths and separate the pale from the dark green. Add the pale to the hot oil together with the garlic, carrot, cucumber, chillis and capsicum. Stir fry for about 5 minutes.
Add the yoghurt, chicken stock, kaffir lime leaves, red curry paste, fish sauce, and sugar and stir vigorously. Bring to a boil and simmer gently for a few minutes until it starts to thicken.
Add the chicken pieces and simmer gently until the chicken is cooked through (about 5 - 7 minutes). Stir in the dark green spring onions leaves and the coriander leaves.