Grilled Chorizo Sandwiches with Chimichurri (Choripán)

Ingredients

• 4 fresh chorizo sausages, Argentinian-style if possible
• Four 6-inch hero rolls, split lengthwise, connected on one side like a hinge
• ¼ cup finely chopped fresh Italian parsley leaves
• ¼ cup minced white onion
• 1 small garlic clove, grated on a microplane
• ¼ cup plus 3 Tbsp. extra-virgin olive oil
• 3 Tbsp. red wine vinegar
• ½ tsp. kosher salt
• ¼ tsp. freshly ground black pepper