01 - In a large mixing bowl, gently combine ground turkey, chopped onion, minced garlic, parsley, Dijon mustard, Worcestershire sauce, salt, and black pepper until just mixed.
02 - Divide the mixture into four equal portions and shape each into patties slightly larger than the burger buns.
03 - Warm the olive oil in a large skillet or grill pan over medium heat.
04 - Cook each patty for 5 to 6 minutes per side until golden brown and reaching an internal temperature of 165°F.
05 - During the last minute of cooking, place a slice of Swiss cheese on each patty and cover with a lid to melt.
06 - Lightly toast burger buns on the skillet or grill until golden and slightly crisp.
07 - Spread mayonnaise on the bottom half of each bun if desired. Layer with lettuce, turkey patty with melted cheese, avocado slices, tomato, and red onion. Top with the remaining bun halves.
08 - Serve immediately accompanied by your preferred side dishes.