To caramelize the apples and onions melt the butter in a large skillet over medium-high heat. Add the onions, apples and 1/4 teaspoon of salt and pepper. Cook, stirring constantly, until the onions and apples begin to soften, about 5 minutes.
Stir in the sugar and cook, scraping the browned bits off the bottom of the pan frequently, until golden brown, about 20 minutes. Set aside.
Toast buns and place aside.
To make turkey mixture, melt butter in a skillet over medium heat. Add celery, scallions, and apples, then cook, stirring, for 15 to 20 minutes. Remove from heat and set aside.
Put chipotle peppers and chutney in blender. Puree until smooth. Transfer to a bowl with turkey, celery mixture, lemon zest, and lemon juice and combine well. Set aside until ready to use.
To make patties, roll six 5-ounce turkey balls and form each ball into a patty. Arrange on a tray, cover, and refrigerate.
Heat large skillet over medium-high heat and add just enough oil to cover bottom. After 2 minutes, reduce the heat to medium, then place patties into the skillet. Season with salt and pepper and cook for 3 minutes, then flip and cook on other side for 1 minute. Place some on the caramelized onions on the patty, then top with the apples and cover with camembert cheese and continue to cook 2 minutes more for medium-rare doneness. Cover with a lid for the last 30 seconds to melt the cheese. Place burgers on toasted buns and serve.