Preheat Oven: Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper or lightly grease it.
Prepare the Marinade: In a small bowl, whisk together the olive oil, balsamic vinegar, soy sauce, minced garlic, dried thyme, black pepper, and a pinch of salt.
Coat the Mushrooms: Place the cleaned mushrooms in a large bowl. Pour the balsamic soy marinade over the mushrooms and toss to coat evenly.
Roast the Mushrooms: Spread the mushrooms in a single layer on the prepared baking sheet. Roast in the preheated oven for 20-25 minutes, stirring halfway through, until the mushrooms are tender and caramelized.
Serve: Remove the mushrooms from the oven and garnish with freshly chopped parsley if desired. Serve warm as a side dish or topping for steaks, chicken, or pasta.