1. Preheat your grill to medium heat (around 375 to 400 degrees Fahrenheit) or your oven to the same temperature.
2. In a large bowl, combine the sliced potatoes and onions. Drizzle with melted butter or olive oil, and add salt, pepper, garlic powder, smoked paprika, and ranch seasoning if using. Toss to coat evenly.
3. Lay out large squares of aluminum foil (heavy-duty recommended) and spray with cooking spray or brush with olive oil.
4. Divide the potato mixture evenly among the foil squares. Optionally add an ice cube to each to prevent burning and ensure moistness.
5. Fold the foil tightly into packets, making sure edges are sealed.
6. Place foil packets on the grill. Cook for 25 to 30 minutes, turning occasionally, until potatoes are tender. If using the oven, bake for about 30 to 40 minutes.
7. Carefully open packets and add shredded cheese and cooked bacon if desired. Close briefly to melt.
8. Top with sour cream, chives, or any other desired garnishes before serving.