Fill a large bowl with ice cubes and cold water and set aside.
Bring a large pot of water to a boil.
Add green beans and cook for about 3 minutes until crisp-tender. Drain beans and immediately place in ice water to stop the cooking.
Melt butter in a large skillet over medium-high heat.
Add garlic and cook for about 1 minute longer until fragrant.
Stir in lemon juice and cook for 1 minute.
Drain green beans and add to skillet.
Saute green beans, stirring occasionally for about 3-4 minutes until heated through.
Remove from heat and stir in Parmesan cheese and lemon zest.
Season with salt and pepper to taste and a pinch of red pepper flakes if desired.
Serve immediately.
