Preheat your oven to 375°F and line a small loaf pan with parchment paper for easy removal.
Finely mince the cremini mushrooms, yellow onion, and garlic until they reach a very small, uniform texture.
In a large mixing bowl, combine the lean ground beef with the minced mushrooms, onion, and garlic.
Add the egg, almond flour, tomato paste, and coconut aminos to the bowl.
Season the mixture with sea salt, black pepper, and dried thyme, then mix by hand until just combined without overworking the meat.
Press the mixture firmly into the prepared loaf pan, smoothing the top with a spatula.
Bake for 35 to 40 minutes, or until the internal temperature reaches 160°F.
Remove from the oven and let the meatloaf rest for 10 minutes before slicing to ensure it remains juicy.