1 Preheat the broiler. Thinly slice the tomatoes. Mince the parsley.
2 In a medium bowl, lightly beat the egg white. Beat in 2 tablespoons of the parsley, the tomato paste, breadcrumbs, 2 of the garlic cloves, the oregano, salt, black pepper and red pepper flakes.
3 Add the veal to the egg-white mixture and mix until well blended. Form the mixture into 24 slightly flattened meatballs (about 1 heaping tablespoon each).
4 In a large nonstick skillet, warm the oil over medium-high heat until hot but not smoking. Add the meatballs and cook until well browned on the outside and medium-rare on the inside, about 6 minutes. Remove the meatballs to a plate and cover loosely to keep warm.
5 Meanwhile, split the rolls in half horizontally (if using long rolls, cut them in half crosswise first). Place them on a broiler pan and broil 4 inches from the heat until toasted, 30 seconds to 1 minute.
6 In a small bowl, combine the remaining parsley, 1 clove of garlic, the mayonnaise, yogurt, lemon juice and lemon zest (if using).
7 Spread the rolls lightly with the lemon-garlic mayonnaise. Top with the tomato slices. Place 6 meatballs in each sandwich.