Place the potatoes in a soup pot with salted water to cover, bring to a boil, and then lower the heat to a rapid simmer and cook, partially covered, for 10 to 15 minutes, or until the potatoes just begin to soften.
In a medium skillet, saute the onions and garlic in the olive oil on low heat. Continue to cook for about 10 minutes, until the onions are translucent.
Add the chili powder and cook for 2 minutes more.
Stir in the tomatoes and bring to a simmer.
Drain the barely tender potatoes and add them to the tomato mixture. Stir to combine and cook until the potatoes are tender, about 12 minutes.
Sprinkle on the parsley, add salt and pepper to taste, and serve piping hot or cool to room temperature.