Preheat the oven to 450 degrees F (220 degrees C). Grease a 9x13-inch baking dish.
Evenly distribute potatoes and onions in the prepared baking dish. Season with garlic powder, kosher salt, and chili powder. Drizzle with olive oil and stir until well coated.
Bake in the preheated oven, stirring every 10 minutes, until potatoes are fork-tender and slightly crispy, 35 to 40 minutes. Remove from the oven and immediately sprinkle Cheddar cheese over top. Let sit until cheese melts, about 5 minutes.