01 - In a large mixing bowl, combine ground turkey, chopped onion, minced garlic, parsley, Dijon mustard, Worcestershire sauce, salt, and black pepper. Mix gently until just combined.
02 - Divide the mixture into 4 equal portions and shape each into a patty slightly larger than the burger 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 fully cooked, reaching an internal temperature of 165°F.
05 - During the final minute of cooking, place a slice of Swiss cheese on each patty and cover with a lid to melt the cheese.
06 - Lightly toast the burger buns on the skillet or grill until warm and slightly crisp.
07 - Spread mayonnaise on the bottom half of each bun if desired. Layer lettuce, turkey patty with melted cheese, avocado slices, tomato, and red onion. Cover with the top half of the bun.
08 - Serve immediately with preferred sides such as a green salad or sweet potato fries.