Make the sauce by whisking the mayonnaise, 2 tablespoons maple syrup and the Dijon mustard together in a small bowl; set aside.
Heat 2 tablespoons canola oil in a frypan over medium heat; cook and stir the onion and about half the chopped apple in the hot oil until soft, 7 to 10 minutes. Set aside.
Mix the remaining uncooked apple, the chicken mince, 2 tablespoons maple syrup, Italian herbs, egg, salt and pepper together in bowl. Shape the burger mixture into 6 balls; the mixture will be loose, but that is okay.
Heat 1 tablespoon canola oil in a large frypan over medium heat. Place one of the balls into the hot oil and flatten with the back of spoon to create a patty. Cook until slightly brown on one side and then flip and cook the other side until cooked through, 5 to 7 minutes per side; repeat for each portion.
To assemble, place the chicken burgers on buns; top with the grilled apple and onions. Pour some sauce over the top of each burger. More sauce can be served on the side if desired.