Preheat grill to medium-high heat. Clean and oil the grates.
Whisk olive oil, lemon juice, zest, garlic, parsley, basil, salt, pepper, and red pepper flakes in a bowl.
Pat shrimp dry with paper towels. Add to the bowl and toss to coat well.
Marinate 15–20 minutes in the refrigerator. Do not over-marinate.
Thread shrimp on skewers or use a grill basket for easy turning.
Grill shrimp 2–3 minutes per side until just opaque and lightly charred.
Brush with melted butter during the last minute for extra richness.
Rest 2 minutes off heat. Taste and adjust salt, then serve hot.