Cook the sausage in a large skillet until done, drain, and place in a mixing bowl. Add the cream cheese, Monterey Jack cheese, and crushed red pepper flakes. Mix well.

Place 1 heaping teaspoon of the mixture into each mushroom cap. Place the stuffed mushroom caps on a rimmed baking pan, sprinkle with Parmesan, and bake for 20 minutes. Remove from oven and let cool for 5 minutes. Serve stuffed mushrooms on a decorative serving platter.