Preheat your oven to 375°F and line a small baking sheet with parchment paper.
In a small skillet over medium heat, sauté the minced onion, garlic, and finely chopped mushrooms until the moisture has evaporated and they are tender.
In a large mixing bowl, combine the lean ground beef, sautéed vegetable mixture, egg, almond flour, coconut aminos, sea salt, and black pepper.
Mix by hand until just combined, being careful not to overwork the meat, then shape into a uniform rectangular loaf on the prepared baking sheet.
In a small bowl, whisk together the tomato paste and balsamic vinegar, then brush the glaze evenly over the top and sides of the meatloaf.
Bake for 25 to 30 minutes or until the internal temperature reaches 160°F.
While the meatloaf rests for 5 minutes, steam the green beans until crisp-tender and serve alongside the sliced loaf.