Begin by cleaning the mushrooms gently with a damp paper towel. Slice them evenly and set aside.
In a large skillet, melt the butter over medium heat. Allow it to cook until it starts to foam and turns a golden brown color, which will take about 5-7 minutes. Watch closely to prevent it from burning.
Once the butter is brown and has a nutty aroma, stir in the minced garlic and fresh thyme. Cook for about 1 minute until the garlic is fragrant.
Add the sliced mushrooms to the skillet, and toss well to coat them in the brown butter mixture.
Season the mushrooms with salt and pepper, and sauté for 6-8 minutes, stirring occasionally, until they are tender and browned.
Remove the skillet from heat and add the lemon zest, mixing well to combine all flavors.
Transfer the mushrooms to a serving dish, and garnish with fresh parsley for a pop of color and flavor.