Grease a baking sheet well, and preheat the oven to 400 degrees.

Finely mince the stems that were removed from the mushroom caps.

Heat the olive oil in a skillet over medium-high heat.

Add the mushroom stems and onion, cooking them until just beginning to soften.

Place the minced garlic into the skillet, and saute for a few seconds before adding the spinach and bacon pieces. Saute until the spinach is wilted.

Add the mixture to a mixing bowl with the pork rind crumbs and parmesan cheese. Stir to combine well.

Stuff each of the mushrooms with the filling mixture, you can heap the filling up above the the mushrooms natural top to get more filling in each one.

Bake for 15 minutes.