To prepare a spicy potato ball recipe, you'll first need to prepare the potatoes. Cut the potato into bite-sized chunks. Place the chopped onion, garlic, chili powder, cumin, salt, and pepper into the bowl of potato puree. Mix the ingredients together until they're well combined. Cover the mixture with plastic wrap and refrigerate for at least 1 hour, or overnight. Preheat the oven to 375?F (190?C) and prepare your oven rack to line the bottom of the pan with foil. Remove the foil and set aside. Heat the oil in the skillet over medium-high heat until shimmering. Add the onion and garlic and cook until the onions are soft and translucent, about 5 minutes. Stir in 1 cup (240 mL) of water and bring to boil. Reduce the heat to medium and simmer until potatoes are tender, 10 to 15 minutes, stirring occasionally. Serve the hot potato balls with sour cream and guacamole.