For the burgers, place the turkey mince with the herbs, onion and garlic powder in a bowl and season with salt and pepper. Carefully mix in the chopped Brie cheese and form into 4 patties. Allow to chill in the fridge for 30 minutes before grilling to your liking. Meanwhile, prepare the stuffing by heating the butter in a pan and soften together the onion, age and chestnuts. Add the chopped bacon to the pan and fry for 3 minutes before adding in the breadcrumbs and enough hot stock to form a mixture that holds its shape firmly. Form into 4 patties and fry or bake in the oven drizzled with oil for 5-10 minutes. For the dressing, drain the pickled onions and chop. Place into a bowl with the mustard, honey and mayonnaise and mix well. Split the buns and toast lightly. Spread with the dressing followed by some salad leaves. Top with a turkey burger and spread with the cranberry sauce. Place the cooked stuffing on top and finish with the grated Cheddar cheese. Place under a hot grill to melt the cheese before serving.