Heat broiler. Place 2 pork tenderloins (1 1/2 pounds each) on a baking sheet. Rub them with 1 tablespoon olive oil; sprinkle with salt and pepper.
Broil 7 minutes. Turn tenderloins; continue broiling until browned and cooked through, about 7 minutes more (a meat thermometer inserted in the center should register 160 degrees) Let rest at least 5 minutes before slicing.
Make the orange-parsley topping: In a small bowl, stir together 1/4 cup finely chopped fresh flat-leaf parsley, 1 1/2 teaspoons minced garlic, and 1 1/2 teaspoons grated orange zest. Season with salt and pepper.
To serve, cut each tenderloin diagonally into thick slices, then sprinkle with the topping.