Heat a medium skillet to medium high heat.
Add 1 tablespoon of coconut oil, once melted add in thinly sliced onions. Saute until lightly caramelized, stirring occasionally. {about 10-15 minutes}
Add in balsamic vinegar. Saute for another 5 minutes, stirring occasionally. Set aside.
Form six 1/4lb. burgers with the lean ground beef.
Lightly season both sides with salt, pepper, and garlic powder.
Heat a large skillet to medium-high heat. Add in 1 tablespoon of coconut oil. Place the burgers in the skillet and saute each side for 3-5 minutes {depending on your desired doneness}.
Remove from skillet and let sit for 1 minute.
Assemble burgers.
Place 1 large slice of beef steak tomato on a plate, top with a pile of shredded lettuce, the burger, 2 tablespoons of the balsamic caramelized onions, and top with sliced avocado {I put half an avocado on each burger}.
Serve with gluten-free mustard.