01 - In a large bowl, gently combine ground turkey, chopped onion, minced garlic, Worcestershire sauce, Dijon mustard, salt, black pepper, parsley, and breadcrumbs if used. Avoid overmixing.
02 - Divide the mixture into 4 equal portions and form each into a patty approximately ½ inch thick.
03 - Heat a grill, grill pan, or skillet over medium-high heat.
04 - Cook each patty for 5–6 minutes on each side until internal temperature reaches 165°F.
05 - During the final 2 minutes of cooking, place a slice of cheddar cheese on each patty and cover to melt.
06 - Slice buns and lightly butter if desired. Toast them on the grill or skillet until golden brown.
07 - Spread mayonnaise, ketchup, and mustard on the bottom buns. Layer lettuce, tomato, and onion slices, then add the cheesy turkey patties. Cover with the top buns.
08 - Serve immediately, pairing with preferred sides.