Combine shrimp, Greek seasoning, lemon juice and zest, mint & parsley in a small bowl. Set aside.
Add olive oil, garlic and red pepper flakes to a large skillet and sauce on medium-high for 30 seconds or so. Add shrimp and butter. Saute for 2-3 minutes until shrimp turns pink. Do not overcook - pre-cooked shrimp only need to be heated up!
Sprinkle some feta on each serving before serving, if desired!