Place the potatoes and 1 1/2 cups water in a 12-inch nonstick frying pan. Cover tightly with a lid or foil and bring to a boil over high heat. Simmer over medium heat until the potatoes are tender when pierced, 5 to 7 minutes.
Drain the potatoes in a colander and wipe pan clean.
To pan, add oil, chili powder, coriander, cumin, and garlic powder; stir over medium-high heat for 30 seconds.
Add potatoes, stir to coat, then mix in tomatoes, 1/4 cup cilantro, and green onions. Over high heat, occasionally turn mixture with a wide spatula until browned, 5 to 6 minutes. Season to taste with salt and sprinkle with a little more cilantro. Offer salsa and sour cream to add to taste.