Melt 3 tablespoons of the butter in a sauté pan over medium heat.
Add the mushrooms in one layer and cook, without moving, until golden brown, about 5 minutes.
Sprinkle with salt and pepper and toss.
Continue to cook until the mushrooms are cooked through, about 5 more minutes.
Add the thyme, garlic and lemon zest, then cook for 1 minute.
Add the lemon juice and remaining tablespoon of butter and toss until the butter is melted.
Sprinkle with the chopped parsley and serve.
