Place the potatoes in a pan of salted water, bring to boil and cook for 10 minutes until just tender. Drain well.
In the meantime, heat the oil in a pan, add the cumin seeds, coriander seeds, turmeric, and sliced chili, and fry over high heat for 1-2 minutes. Add onions and continue to cook over a medium heat until onions are soft and transparent. Add the drain potato cubes and a little water, stir well cover and cook for 10 minutes, stirring from time to time.
Add the contents of the tin of tomatoes, mix well and continue to cook for 5minutes. Serve hot.

1 pound potatoes, peeled and cut into 1 inch cubes
salt
1 teaspoon turmeric
4 tablespoon vegetable oil
2 green chilis, de-seeded and thinly sliced
2 onions, sliced
1/2 teaspoon coriander seeds
1/2 teaspoon cumin seeds
7 ounce can chopped tomatoes