Step 1

In a medium bowl, toss the shrimp with 2 tablespoons of the olive oil and the crushed red pepper; season with salt and black pepper. Let stand for 20 minutes.

Step 2

Heat a large skillet until very hot. Add the shrimp and cook over high heat until lightly browned and nearly cooked through, about 2 minutes. Transfer the shrimp to a plate.

Step 3

Add the remaining 2 tablespoons of olive oil to the skillet along with the pancetta, onion and garlic and cook over high heat, stirring occasionally, until lightly browned, about 4 minutes. Return the shrimp and any accumulated juices to the skillet. Add the marinara sauce and simmer over moderate heat until the shrimp are cooked through, about 2 minutes. Transfer the shrimp to bowls, garnish with the parsley and serve with crusty bread.