Place potatoes in a saucepan and cover with cold water. Bring to a boil, reduce heat and simmer 15-20 minutes or until potatoes are tender. Drain; mash with a potato masher or pass through a ricer.
In a skillet, heat oil over medium heat. Add onion, ginger and garlic; cook, stirring frequently, until onion starts to brown.
Stir in chili powder, coriander, cumin and salt; cook for 1 minute. In a bowl, fold together potatoes, onion mixture and cilantro. Form into 8 patties. (May be done ahead of time and refrigerated until needed.)
Heat a skillet or griddle and coat lightly with cooking spray. Fry patties 3-4 minutes on each side or until golden brown. Serve with yogurt, if desired.