01 - In a large bowl, combine the ground turkey, finely chopped onion, minced garlic, fresh parsley, Worcestershire sauce, Dijon mustard, salt, and black pepper. Mix gently until just combined, taking care not to overwork the meat.
02 - Divide the prepared mixture into 4 equal portions. Shape each portion into a patty, ensuring they are slightly larger than your burger buns to account for shrinkage during cooking.
03 - Heat 1 tablespoon of olive oil in a large skillet or grill pan over medium heat.
04 - Place the turkey patties in the heated skillet. Cook for 5 to 6 minutes per side, or until they are golden brown and an internal temperature of 165°F (74°C) is reached.
05 - During the final minute of cooking, place one slice of cheddar cheese on top of each patty. Cover the pan briefly to allow the cheese to melt thoroughly.
06 - If desired, lightly toast the burger buns until golden brown.
07 - To assemble, place a lettuce leaf on the bottom half of each toasted bun. Top with a turkey patty (with melted cheese), a slice of tomato, and a slice of red onion. Add mayonnaise or ketchup to taste, if using. Cover with the other half of the bun.
08 - Serve the turkey burgers hot and fresh.