Preheat the oven to 400 degrees. Coat a baking sheet with olive oil cooking spray.
Place the mushrooms in the center of the baking sheet, drizzle with olive oil, add fresh thyme leaves, then season with sea salt and freshly cracked pepper to taste; toss to coat evenly.
Spread the mushrooms in a single layer on the baking sheet and top with a sprig of fresh thyme.
Roast for 10 minutes, then flip them with a spatula and cook for another 10 minutes, or until golden brown.
Place the minced garlic into the melted butter; set aside.
Remove the mushrooms from the oven, drizzle the melted garlic butter on top, then return to the oven for 3-5 minutes.
Remove from the oven, squeeze juice and zest from ½ a lemon over the mushrooms, and top with a few more fresh thyme leaves; toss to coat evenly.
Place in a serving bowl with lemon wedges on the side.