In a large bowl, combine the potatoes, onion, garlic and olive oil. Toss to coat the vegetables.
Add in the rosemary, smoked paprika, salt and pepper, and toss to coat again.
Using 2 pieces of foil (each 24 inches long), form an X by overlapping the foil.
Place the potato mixture in the middle of the X, arranging so that it is an even height. Wrap the pieces of foil over the potato mixture, pinching the foil to seal.
Use a third piece of foil to wrap around the package.
Place the foil package on the grill and cook for 20 minutes. Flip the package over and cook for an additional 15 to 20 minutes, or until the potatoes are tender and starting to brown. Be careful when opening the package to test the vegetables, as hot steam will be released.
The vegetables will stay warm in the package for 10 to 15 minutes. Serve.