Melt 2 tbsp butter in a large stock pot over med heat. Add 4 cloves minced garlic and let sizzle for about 30 seconds. Season with 1/2 tsp red pepper flakes and lemon zest, stirring for about 45 seconds. Quickly pour in 2 c white wine into the pan and season with black pepper. Bring sauce to a boil, stir in 2 lbs mussels, and cover immediately. Stir mussels, replace cover, and let boil until shells open. Stir in chopped. Serve with grilled bread and lemon wedge.