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