Preheat grill to 500 degrees F. Spray with non- stick spray
Mix sirloin, egg, bread crumbs and chopped beets together. Form 6 patties.
Spray a large square of (approximately 10" X 10") of aluminum foil with non-stick cooking spray. Peel and slice apples into quarters then thinly slice. Cut onions into circles, then halves. Wrap up into a packet by placing apples and onions in the middle and then fold edges over to make a square and seal off the sides.
mix all ingredients together and top burgers with ½ of the sauce. Grill burgers for 10 -15 minutes (with barbecue lid down) , then turn over. Top burgers with remaining sauce and cook for 10 – 15 minutes.
Meanwhile, while burgers are cooking, roast apple/onion mixture in packets on grill (back of grill where there is less heat) for approximately 20 minutes.
Turn off grill, add Brie cheese and cover until melted (about 1 minute), then grill buns for 2- 3 minutes or until grill marks are to your liking.
Mix cosmo cranberry aoili ingredients together and spread 2 tsps on bottom of grilled bun. Add burger, spinach, then ¼ cup roasted apple/red onion mixture. Mix balsamic vinegar and greek yogurt together and put a dollap (about 2 tsp ) on top of apple/onions. Add top of bun. Serve immediately and enjoy!