Preheat your oven to 375°F and line a small loaf pan with parchment paper for easy removal.
Finely mince the white mushrooms, yellow onion, and garlic to ensure they blend seamlessly into the meat.
In a large mixing bowl, combine the ground beef, egg, minced mushrooms, onion, garlic, sea salt, black pepper, and dried oregano.
Gently mix the ingredients by hand until just incorporated, taking care not to overwork the meat which can lead to a tough loaf.
Press the mixture into the prepared loaf pan, smoothing the top into an even shape.
In a small bowl, whisk together the tomato paste, coconut aminos, and apple cider vinegar to create a thick, tangy glaze.
Spread the glaze evenly over the top of the meatloaf using a spoon or brush.
Bake for 35 to 40 minutes, or until the internal temperature reaches 160°F.
Remove from the oven and let the meatloaf rest for 5 to 10 minutes before slicing to lock in the juices.