Split rolls in half. Hollow out top and bottom halves of the rolls, leaving a 1/2-inch-thick shell; reserve torn bread for another use. Combine vinegar, oil, and garlic; stir with a whisk. Spoon vinegar mixture evenly over cut sides of rolls.
Combine juice, parsley, black pepper, and tuna. Spoon 1/2 cup tuna mixture on bottom half of each roll. Layer bell pepper slices, tomato slices, spinach leaves, anchovies, and onion over tuna mixture. Cover with tops of rolls. Wrap each roll tightly with plastic wrap, and refrigerate 2 hours or overnight.