Preheat your oven to 375°F and line a small baking dish with parchment paper.
Heat the olive oil in a small skillet over medium heat, add the diced onions, and sauté until they are golden brown and caramelized.
In a medium mixing bowl, combine the lean ground beef, egg, almond flour, sautéed onions, sea salt, black pepper, and garlic powder.
Mix the ingredients by hand until just combined, being careful not to overwork the meat.
Shape the mixture into a uniform loaf and place it in the prepared baking dish.
In a small ramekin, whisk together the tomato paste and balsamic vinegar until smooth.
Brush the glaze evenly over the top of the meatloaf.
Bake for 25 to 30 minutes, or until the internal temperature reaches 160°F.
Let the meatloaf rest for 5 minutes before slicing to ensure it stays juicy.