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