Mix together the garlic, salt, pepper, and vinegar. Marinate the pork cubes in the refrigerator in this mixture for at least 3 hours.
Heat up the grill, and thread on 8 skewers a piece of pork, a few squares of prosciutto, a sage leaf, a few layers of the onion, and a mushroom. Continue in this manner until all the ingredients are used.
Brush the skewers lightly with the oil, season with additional salt and pepper, and grill until the pork is golden brown, about 10 minutes per side.