1. Wash mushrooms, finely chop thyme and mince garlic.
2. In a bowl, combine olive oil, lemon juice, minced garlic, finely chopped thyme, salt and pepper.
3. Preheat oven to 400 degrees F (200 degrees C). Line a baking sheet with aluminum foil.
4. Place mushrooms in a bowl and toss.
5. Transfer mushrooms to the baking sheet. Top with butter slices.
6. Bake in the preheated oven for 8 minutes, flip and cook for another 5 minutes.
7. Drizzle cooking juices over mushrooms, sprinkle with parsley and serve.