Since it's leaner, fat is important to making turkey burgers awesome, either in the patty or as a topping.
Also, I find letting a turkey burger be "its own thing" vs a "replacement for a beef burger" is also important for getting folks to love them. So, it's never pickles/onions/ketchup/mustard as a combo on my turkey burger b/c that's so classic on beef...Instead, it's:
A turkey club burger (topped with bacon, avocado, lettuce, tomato, onion, and mayo or dijoniase)
Or a Thanksgiving burger (topped with cranberry aoili and served OR topped with sweet potato chips/fries)
Or turkey maple bacon (topped with brown sugar bacon and a maple aoili)
Cheese should be American or Harvarti or Pepper Jack - those cheeses you like naturally with turkey, depending on the burger (I can't have cheese, so I lean on the avocado and mayo and the bacon options for my fat)...