If using wooden skewers, soak them in water for at least 30 minutes to prevent burning on the grill.
In a large bowl, whisk together the balsamic vinegar, olive oil, minced garlic, dried oregano, salt, and black pepper.
Add the cleaned mushrooms to the bowl and toss until they are well coated in the marinade. Let them marinate for at least 15 minutes for the best flavor.
Preheat your grill to medium-high heat.
Thread the marinated mushrooms onto the skewers, leaving a little space between each mushroom for even cooking.
Place the skewers on the grill and cook for about 8-10 minutes, turning occasionally, until the mushrooms are tender and have nice grill marks.
Remove the skewers from the grill and sprinkle with fresh parsley before serving.