Preheat the oven to 200 C.
Heat the oil in a wok over a medium heat, and add mustard seeds, cumin seeds, dried chillis, curry leaves and Asafoetida.
When the mustard seeds start to pop and splutter, add finely chopped onions and fry for 3 minutes over a medium heat. Add the grated ginger and crushed garlic and fry for a further two minutes until the onions are a light brown in colour.
Add the diced potatoes, and fry for 3 minutes.
Add the Tumeric, Garam Masala, Ground Coriander and Dried Mango powder and mix to coat the potatoes.
Transfer the whole lot into a roasting tin, and season well with salt.
Roast in the oven for about 45 mins until potatoes are cooked through