Heat a large skillet over medium heat and add olive oil.
Add minced garlic to the skillet and sauté for about 30 seconds, until fragrant.
Add the spinach to the skillet, stirring constantly, until it starts to wilt, about 2-3 minutes.
Add salt, lemon juice, butter, black pepper, and red pepper flakes (if using) to the skillet. Stir to combine and continue to cook for another 2-3 minutes, or until the spinach is fully wilted and the flavors have melded.
Remove from heat and sprinkle with grated Parmesan cheese (if using).
Serve hot and enjoy as a side dish or as a healthy, flavorful addition to any meal!