You can substitute 1 tablespoon curry powder for the spices.

1/3 c vegetable oil
1 t cumin seeds
1 t ground coriander
1/2 t mustard seeds
1/2 t ground turmeric
2 medium onions, thinly sliced
2 T chopped jalapeno chiles with seeds
1-1/2 lbs potatoes, cut in 1/2-inch dice
1-1/4 c chopped tomatoes, (about 2 medium)
salt and pepper. to taste

1. Heat oil in a large skillet over medium heat for about a minute. Add cumin seeds, coriander, mustard seeds, and turmeric to skillet. Cook until the seeds are fragrant and darken slightly, stirring, about 2 minutes. You may need to turn the heat down some to prevent burning.

2. Add onions and jalapenos; sauté until onions soften, about 5 minutes. Add potatoes and stir until well coated with spice mixture. Cover and cook until potatoes are almost tender, stirring occasionally, about 10 minutes. Add chopped tomatoes; cover and cook until potatoes are tender, about 7 or 8 minutes longer. Season to taste with salt and pepper.