Preheat the olive oil in a large skillet over medium-high heat. Add the mushrooms to the HOT pan and let them sit for 2 minutes before flipping them to brown on the other side for 2 minutes.
Add the minced garlic, crushed red pepper flakes, and spinach to the skillet. Add a tablespoon of water and cook, stirring constantly for 1-2 minutes, or until the spinach is just wilting. Season with sea salt and freshly cracked pepper, to taste.
Pour into a serving bowl and top with shaved Parmesan. For a little extra flavor, add a drizzle of balsamic vinegar, if desired. Serve immediately. Enjoy.