Interesting and different proposal for an appetizer
Cut the shrimp into skewers (optional).
Put the olive oil, basil, garlic, red pepper flakes, salt, parmesan and walnuts in a food processor and process until the mixture is homogeneous.
Keep two tablespoons of pesto in a bowl large enough to fit all the shrimp and set aside.
Drizzle the shrimp with the remaining pesto and leave to marinate at room temperature for about 30 minutes.
Lightly grease a grill and preheat over medium to high heat.
Place the shrimp on the grill and cook for a few minutes on each side. Transfer the cooked shrimp to the bowl with the kept pesto and stir to cover evenly. Serve immediately.