Preheat oven to 400°F (200°C). Line a large rimmed baking sheet with parchment paper.

Gently wipe mushroom caps clean with a damp paper towel. Pop out the stems. Finely chop 1/2 cup of the stems for the filling. Toss hollowed mushroom caps in 2 tablespoons olive oil, a pinch of salt, and pepper. Arrange cavity-side up on the baking sheet.

In a small skillet over medium heat, melt 1 tablespoon butter. Sauté the minced mushroom stems and minced garlic for 2 minutes until tender and fragrant. Remove from heat and cool for 5 minutes.

In a mixing bowl, beat softened cream cheese, sautéed garlic-stem mixture, grated parmesan, fresh parsley, fresh thyme, onion powder, and black pepper until creamy and thoroughly blended.

Use a small spoon or cookie scoop to mound generous portions of the cream cheese filling into each mushroom cap.

In a small bowl, stir together panko breadcrumbs, melted butter, 2 tablespoons parmesan, and parsley until moist and clumpy. Press a pinch of panko topping onto each stuffed mushroom.

Bake at 400°F (200°C) for 18 to 20 minutes, until mushroom caps are tender and juicy, the cheese filling is hot and bubbling, and the panko topping is deeply golden brown and crisp.

Rest for 5 minutes before serving warm on an appetizer platter garnished with fresh thyme and lemon wedges.