01 - In a large bowl, combine ground turkey, onion, garlic, parsley, Worcestershire sauce, Dijon mustard, salt, and pepper. Mix until just combined; do not overwork.
02 - Divide the mixture into 4 equal portions and shape into patties, slightly larger than the buns.
03 - Heat olive oil in a large skillet or grill pan over medium heat.
04 - Cook the patties for 5–6 minutes per side, or until the internal temperature reaches 165°F and they are golden brown.
05 - Place a slice of cheese on each patty during the last minute of cooking. Cover the pan to melt the cheese.
06 - Lightly toast the burger buns, if desired.
07 - Place a lettuce leaf on the bottom half of each bun, followed by the turkey patty with melted cheese, tomato slice, and red onion. Add mayonnaise or ketchup if desired. Top with the other half of the bun.
08 - Serve immediately while hot.