Preheat oven to 425 degrees. Line baking sheet or pan with parchment paper. Depending on the size of your mushrooms, halve them or quarter them. Place on baking sheet.
Drizzle olive oil, balsamic vinegar, salt and pepper on top of the sliced mushrooms and toss to coat.
Bake 15-20 minutes until they are done. Sprinkle with parsley.
Serve warm.