Cut potatoes into 3/4 inch cubes. Heat the mustard seeds in dry pan until they start to pop. Add ghee, onions, garlic and ginger; cook, stirring until soft. Add turmeric, salt, pepper, chili, cumin, garam masala and potatoes. Stir until potatoes are coated. Add water and simmer, covered, for 15-20 minutes or until potatoes are just tender; stir occasionally. Add peas and stir. Simmer, covered, for 3-5 minutes or until potatoes are cooked through and liquid is absorbed. Add cilantro and stir.