In a small bowl, combine the garlic, salt & pepper. Set aside. Heat a large skillet or sauté pan over medium-high heat for 1 to 2 minutes. Add the oil to the pan and allow to heat up for ~20 seconds.
Add the mushrooms to the pan. Use a wooden spoon to stir the mushrooms & coat with the oil. Cook the mushrooms, stirring occasionally, until they are cooked through and lightly browned ~5 minutes.
Add the garlic mixture to the pan and cook, stirring continuously, for 1 minute. Add the lemon juice or balsamic vinegar (if using), and stir.
Turn off the heat and stir in the parsley (if using). Serve immediately and enjoy!