In a medium bowl, whisk together ¼ cup Dijon mustard, ¼ cup maple syrup, and ¼ cup mayonnaise until smooth. Cover and refrigerate.

In a large skillet over medium heat, add 4 slices of chopped bacon and cook until crispy, about 4-5 minutes. Remove the bacon and reserve drippings.

In the same skillet, add ½ cup minced red onion and 2 minced garlic cloves. Sauté for about 2 minutes until the onion is translucent.

Pour in ¼ cup apple juice to deglaze the pan, scraping up browned bits. Simmer for 2-3 minutes, stirring occasionally. Add in the bacon, one chopped apple, and 1 tablespoon dried sage, cooking for 2 more minutes.

In a large bowl, mix the cooled apple mixture with 1 cup panko and 1 pound ground chicken until just combined. Shape into 6 patties and refrigerate for 30 minutes.

Preheat the grill to medium-high heat. Cook the patties for 6-7 minutes on one side, flip and cook for another 6-8 minutes until the internal temperature reaches 165°F. Melt cheese during the last minute.

Toast the brioche buns and spread sauce on the bottom. Add grilled patties, lettuce, and red onion before topping with the other bun.