Gently clean the mushrooms with a damp cloth, then trim the stems and scrape out the gills with a spoon to remove excess moisture and improve grill results.
Mix olive oil, balsamic vinegar, minced garlic, salt, pepper, and herbs in a small bowl to create the marinade.
Brush the cleaned mushroom caps generously with the marinade, ensuring all surfaces are coated evenly and let them sit for 10-15 minutes to absorb the flavors.
Preheat your grill or grill pan over medium-high heat until hot, and lightly oil the grates to prevent sticking.
Place the mushroom caps onto the hot grill, gill side down first, and listen for a satisfying sizzle. Grill for about 4-5 minutes, watching for deep grill marks and a slight char.
Flip the mushrooms carefully using tongs, and cook for another 4-5 minutes until tender, with visible grill marks and a fragrant smoky aroma.
During the last minute, brush the mushrooms with a little extra marinade or balsamic glaze for added flavor and shine.
Remove the mushrooms from the grill and squeeze fresh lemon juice over them for brightness, if using. Let them rest for a minute to absorb the flavors.
Serve the grilled portobello mushrooms hot, garnished with fresh herbs if desired, and enjoy their juicy, smoky, and savory goodness.
