Heat the oil in a large non-stick frying pan over a low heat. Add the garlic, ginger, fennel, cumin and turmeric. Cook for 1 minute.
Add the potatoes and shake the pan to coat them with the spice mixture. Cook for about 5 minutes or until they begin to turn golden brown. Add the water, cover the pan with a lid and cook, shaking the pan occasionally, for about 30 minutes or until the potatoes are tender.
Remove and discard the ginger. Sprinkle the lemon juice over the potatoes. Serve the garlic cloves in their skins; each diner can then squeeze the creamy roasted garlic from its skin onto the potatoes to add flavour.