Add ingredients to a jar with a tight fitting lid, or in a bowl, then shake or whisk to combine. Refrigerate until ready to use — can be made up to a week ahead of time.
For the Caramelized Onions:
Heat olive oil in a large pot or skillet over medium heat. Add onions, season with salt and pepper, then cook, stirring every so often until onions are a rich caramel brown color and are sticky and caramelized, 20-25 minutes. Scoop into a bowl then set aside.
For the Orchard Turkey Burgers:
Add ground turkey to a large mixing bowl with grated apple, dried thyme, garlic powder, onion powder, and salt and pepper. Use your hands to mix until jut combined then form the mixture into 4 patties. Brush the patties with extra virgin olive oil.
Heat a large skillet over medium-high then add turkey burgers and cook for 4-5 minutes a side, or until no longer pink in the center. Top each burger with 1/4 of the brie then place a lid on top, or tent with foil, to melt.
Divide lettuce among plates then top with apple slices, burgers, and caramelized onions. Drizzle with honey mustard vinaigrette and serve.