Line a tray or baking sheet with parchment paper.
Finely grate the onion and squeeze out as much moisture as possible using paper towels.
In a large mixing bowl, combine the ground turkey, grated onion, garlic, mayonnaise, Worcestershire sauce, salt, and black pepper.
Gently mix until just combined. Avoid overmixing to keep the burgers tender.
Divide the mixture into four equal portions and shape into 1-inch thick patties.
Place the patties on the prepared tray and freeze for 20 minutes to help them firm up.
Meanwhile, preheat the grill to medium-high heat (about 450–500°F / 230–260°C).
Clean the grill grates thoroughly and lightly oil them to prevent sticking.
Remove the chilled patties from the freezer and gently press a small indentation into the center of each patty with your thumb.
Grill the Best-Ever Grilled Turkey Burgers for 6–7 minutes per side, or until the internal temperature reaches 165°F (74°C).
If using cheese, place a slice on each burger during the final 2 minutes of cooking.
Serve on toasted buns with your favorite toppings and condiments.