Heat the oil in a saucepan and brown the onions. When they are golden put the fenugreek and cumin seeds and stir until they turn a shade or two darker. Put the garlic, haldi, red chilli powder and salt and stir together for a few minutes. Put the chopped potatoes and green peppers and simmer over low heat in a covered pan. After 5 minutes, put the tomatoes, replace the lid and cook until both the potatoes and peppers become tender. Stir in the fresh coriander before removing from the heat to serve.