Put the chicken in a single layer in a wok or large frying pan over a medium heat, with just enough water to cover. Crumble in the stock cube and add 1 teaspoon of the curry powder. Simmer gently, stirring, for about 10 minutes, until the chicken is no longer pink.
Stir in the chopped vegetables and garlic. then another 1 teaspoon curry powder. Simmer gently for a further 20 minutes, stirring occasionally.
Crumble in the creamed coconut and stir to dissolve. This should thicken the cooking liquid so that it is no longer watery. (If the stock is too thin, the yogurt will curdle when you add it.) If it still appears quite watery, simmer for a little longer until it thickens, or dissolve 1 teaspoon cornflour in a little cold water and mix it in.
Reduce the heat to low, and stir in the remaining curry powder, sugar and paprika.
Gradually mix in the yogurt and heat through, stirring, for about 5 minutes. Add salt and pepper to taste.
Creamed coconut is available inexpensively from most Asian or Indian shops, either in 200g blocks or in a box of 4 convenient 50g sachets.