Scrap the skin of the potatoes and chop them into cubes. Pressure cook them till they are soft and firm. In a kadai heat the oil. Add the mustard seeds. When they splutter add the cumin seeds, curry leaves, chopped onions and keep sautéing till the onions turn pink and soft. Now add the turmeric powder, potato cubes, salt, pepper powder and mix well. Cook for 5 mins and serve garnished with chopped coriander and a dash of lemon squeezed over it.