01 - Combine ground turkey, breadcrumbs, egg, red onion, garlic, Worcestershire sauce, salt, and pepper in a large bowl. Mix gently until just combined; avoid overmixing to prevent tough patties.
02 - Divide mixture into 4 equal portions and form into patties approximately 1/2 inch thick. Make a slight indentation in the center of each patty to prevent puffing during cooking.
03 - Heat grill or skillet over medium-high heat. Lightly oil the surface to prevent sticking.
04 - Place patties on the preheated surface and cook for 5 to 6 minutes per side. Cook until fully cooked through, reaching an internal temperature of 165°F.
05 - During the final minute of cooking, place a slice of Swiss cheese on each patty. Cover with a lid to allow the cheese to melt completely.
06 - Toast the split burger buns cut side down until golden and lightly crisped.
07 - Spread mayonnaise and/or mustard on the toasted buns as desired.
08 - Layer each burger with lettuce, turkey patty with melted cheese, avocado slices, and tomato. Place the top bun and serve immediately.