Begin by cleaning the mushroom caps gently with damp paper towels to remove any dirt, then place them in a shallow dish.
In a small bowl, whisk together olive oil, balsamic vinegar, minced garlic, chopped herbs, salt, pepper, and optional smoked paprika until well combined.
Pour the marinade over the mushroom caps, using a brush or your fingers to coat them evenly on all sides. Let them sit for at least 15 minutes to soak up the flavors.
Preheat your grill to a high, steady flame, until you hear a consistent sizzling sound and see the metal grates glowing slightly.
Place the marinated mushroom caps on the hot grill, with the gill side down if applicable, and press gently with tongs to ensure even contact and searing.
Grill for about 4-5 minutes, watching as the caps soften, develop deep grill marks, and the edges darken slightly with a hint of char.
Use tongs to flip the mushrooms carefully, then continue grilling for another 4-5 minutes until they are tender and fragrant with smoky aroma.
Once cooked through and nicely charred, remove the mushrooms from the grill and let them rest for a couple of minutes to settle the flavors.
Serve the grilled Portobello mushrooms hot, drizzled with any remaining marinade or fresh herbs, for a hearty and smoky vegetarian dish.
