Peel onions, cut in half, and then thinly slice your onions (half moons).
Heat up 1-2 tbsp of avocado oil in a large pan over medium heat and add onions. Cook for 12-15 min, until browned, reduced in size by about half, and caramelized. Add balsamic, stir in, and remove from heat. Let cool slightly before adding to meat.
Combine meat, egg, breadcrumbs, French onion soup mix, dried thyme, and beef broth and mix well. Add 3/4 of your onion mixture and mix well.
Add meatloaf mixture to a well-greased and parchment-lined 9x5 loaf pan, patting it smooth, and top with remaining caramelized onions.
Top with gruyere and bake for 45 min to 1 hour, until the internal temperature reaches at least 160F.
Slice into 6 slices and serve with your choice of sides. Enjoy!