01 - Combine ground turkey, breadcrumbs, egg, minced shallot, garlic, Dijon mustard, salt, pepper, and parsley in a large bowl. Mix gently until just incorporated, being careful not to overwork the meat.
02 - Shape the mixture into 4 equal patties, making them slightly larger than your burger buns to account for shrinkage during cooking.
03 - Heat olive oil in a large skillet or grill pan over medium heat. Place patties in the pan and cook for 5 to 6 minutes on the first side until well browned.
04 - Flip patties and top each with a slice of Swiss cheese. Continue cooking for 4 to 5 minutes more until cheese is melted and internal temperature reaches 165°F.
05 - Lightly toast the split burger buns and spread mayonnaise on the bottom halves if desired.
06 - Layer lettuce leaves and tomato slices on the bottom bun. Place the cooked turkey patty with melted cheese on top, add avocado slices, and cover with the top bun.
07 - Serve immediately while hot, accompanied by sweet potato fries or a fresh green salad.