Preheat the oven to 400 degrees F (200 degrees C). Line a baking sheet with parchment paper.
Wipe mushrooms clean with a damp paper towel and place in a bowl. Add vinegar, oil, garlic powder, salt, and pepper; stir to combine. Let sit while oven preheats.
Place mushrooms in a single layer on the prepared baking sheet.
Bake in the preheated oven for 20 minutes. Remove baking sheet from oven and garnish with chives.