Grab a large pan. Add oil and heat over medium. Once the oil is shimmering, add mushrooms, salt, and pepper, and toss to coat. Spread mushrooms into a single layer (or as close as you can get), and cook for 3-4 minutes--you'll know they're done once they have a golden sear.
Use a spatula or spoon to flip the mushrooms as best you can (you probably won't flip all of them, the goal is to sear each side). Cook on the second side for another 3 minutes, or until this side has browned.
Reduce the heat of your pan a little, and add the butter and garlic. Toss to coat the mushrooms as the butter melts. Continue to cook until the mushrooms have softened to your liking--for us, this is about 3 more minutes. Stir in the garlic and saute until fragrant, about 30 seconds.
Remove mushrooms from heat, and stir in the thyme. Serve warm and enjoy!