Put oil into skillet and add mustard and cumin seeds. When they start to sputter, add onion, garlic and ginger. Saute until golden brown, about 5 minutes.
Add tomatoes and peas and cook until tomatoes are cooked.
Add potatoes, salt, red chile powder, coconut powder, turmeric and garam masala. Add 1/4 c water. Cook, covered, over med heat until potatoes are cooked through, stirring occasionally, about 10-15 minutes.