Preheat your grill to a medium-high heat and prepare the mushrooms by wiping them with a paper towel to remove any dirt.
Use a sharp knife to scrape out the gills from underneath each mushroom cap, creating space for seasoning and toppings.
Brush both sides of the mushroom caps generously with olive oil using a basting brush, ensuring they are evenly coated and shiny.
Sprinkle the minced garlic, salt, and pepper evenly over the caps, pressing lightly so the flavors adhere.
Place the mushrooms gill-side down on the hot grill and cook for about 4-5 minutes, until they start to brown and release sizzle sounds.
Flip the mushrooms carefully and cook for another 4-5 minutes, basting with a little more oil if needed, until they are tender and caramelized on the surface.
During the last minute of grilling, drizzle the balsamic vinegar over the caps and sprinkle with fresh thyme or rosemary for aroma and flavor.
Remove the mushrooms from the grill and let them rest for a minute. If desired, sprinkle with crumbled feta or Parmesan cheese while still hot to allow it to melt slightly.
Serve the grilled Portobello mushrooms hot, with their smoky aroma and tender, juicy texture ready to enjoy.
