1. Bring a large pot of water to a boil. Add green beans and cook for 3-4 minutes until bright green and just tender. Drain and plunge into ice water to stop the cooking. Drain again and set aside.

2. In a large skillet over medium-high heat, add 1 tablespoon olive oil. Once hot, add the sliced mushrooms in a single layer. Cook undisturbed for 3-4 minutes to develop a golden sear, then stir and cook another 2-3 minutes until softened.

3. Reduce heat to medium. Add the butter and minced garlic to the pan with mushrooms. Stir constantly for 1-2 minutes until the garlic is fragrant and the butter is fully melted.

4. Add the blanched green beans to the skillet. Toss everything together for 2-3 minutes until heated through and well coated in the garlic butter sauce.

5. Season with salt, pepper, and freshly chopped parsley. Serve immediately.