A few key ingredients transform this simple burger into something truly juicy and delicious.
Combine turkey, grated onion, ketchup, Worcestershire, dry mustard, salt and pepper in a medium bowl. Add breadcrumbs and mix with your hands until just combined. Divide the mixture into 4 burgers, 1/2 inch thick. Cover and refrigerate for at least 15 minutes or up to 8 hours.
Meanwhile, preheat grill to medium-high.
Oil the grill rack. Grill the burgers, flipping once, until an instant-read thermometer inserted in the center registers 165°F, about 4 minutes per side. Transfer to a clean plate and let rest for 5 minutes. Serve on buns with lettuce, red onion and tomato, if desired.
Refrigerate burgers (Step 1) for up to 8 hours.