Soak the skewers: If using wooden skewers, soak in water for at least 20 minutes to prevent burning.
Make the marinade: In a large bowl, whisk together olive oil, garlic, lemon zest, lemon juice, parsley, salt, pepper, and red pepper flakes.
Marinate the shrimp: Add shrimp and toss gently until evenly coated. Cover and refrigerate for 15–30 minutes (do not exceed 2 hours).
Preheat grill: Heat grill to medium-high (about 400°F / 200°C).
Thread the shrimp: Skewer shrimp, piercing near the tail and head so they lay flat. Alternate with vegetables if using.
Grill: Place skewers on the grill. Cook 2–3 minutes per side, until shrimp are pink, opaque, and lightly charred. Internal temperature should reach 120–125°F (49–52°C). Avoid overcooking.
Remove from grill and rest for 2 minutes.
Garnish with fresh parsley, a squeeze of lemon, and a light drizzle of olive oil before serving.