Remove stems from mushrooms. Using a spoon, scrape out and remove dark brown gills; discard gills. Whisk together vinegar, oil, miso paste, soy sauce, garlic, brown sugar, salt, pepper and chili flakes; brush over mushrooms. Marinate for at least 1 hour or up to overnight.
Preheat grill to medium-high heat; grease grate well. Grill mushrooms for 3 to 4 minutes per side or until grill-marked and tender. Sprinkle with chopped parsley.
Filippo Berio’s classic, balanced Extra Virgin Olive Oil. Taken from the first cold pressing of the olives, this oil is ideal for sauces, marinades, drizzling and dipping.