Heat oil in a large saucepan over medium heat. Add onions and bell pepper.
Saute till cooked, stirring frequently. Add the remaining ingredients, except yoghurt, adding small amounts of water if necessary. Mix well.
When the mixture comes to a boil, reduce heat and cover and cook for about 45 minutes or until the potatoes are cooked. Keep stirring while cooking.
Serve over noodles or rice and top each serving with 2 tablespoonfuls of yogurt.
If using noodles, cook noodles and add butter and parsley to hot noodles before serving.