In a large bowl, combine the ground turkey, breadcrumbs, Parmesan cheese, parsley, red onion, garlic, egg, Dijon mustard, Worcestershire sauce, salt, and pepper. Mix gently until just combined — do not overmix.
1 pound ground turkey, ½ cup breadcrumbs, ¼ cup grated Parmesan cheese, ¼ cup fresh parsley, ¼ cup red onion, 1 clove garlic, 1 large egg, 1 tablespoon Dijon mustard, 1 tablespoon Worcestershire sauce, 1 teaspoon salt, ½ teaspoon black pepper