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 olive oil, balsamic vinegar, minced garlic, oregano, thyme, salt, and black pepper.
Add the cleaned mushrooms to the bowl and toss until they are well coated in the marinade. Cover and let marinate in the refrigerator for at least 30 minutes, or up to 2 hours for more flavor.
Preheat the 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 10-12 minutes, turning occasionally, until the mushrooms are tender and have nice grill marks.
Remove the skewers from the grill and let them rest for a few minutes. Garnish with fresh parsley before serving.