Preheat the air fryer to 375°F for 5 minutes. While the air fryer is preheating, thoroughly mix the ground turkey, grated onion, ketchup, soy sauce, dijon mustard, and seasonings in a large mixing bowl. Shape the burger mixture into 4 equal-sized, ½-inch thick patties. The mixture will be a little soft and loose - that's okay.
1 ¼ pounds ground turkey, ¼ large yellow onion, 2 tablespoons ketchup, 1 tablespoon low-sodium soy sauce, ½ tablespoon dijon mustard, ½ teaspoon garlic powder, ½ teaspoon onion powder, ¼ teaspoon kosher salt, ¼ teaspoon black pepper