Thinly slice the mushrooms on a mandoline, or slice as thinly as you can if you don't have one.

Scatter on a rimmed platter or plate.

Chop bacon and cook in a skillet over medium heat until the fat renders and the bacon is crisp, about 8 minutes.

Add cider vinegar and olive oil to the skillet and stir.

Pour bacon dressing over the mushrooms and toss to coat.

Finish with the arugula or flat parsley leaves, Parmesan, and pepper.