In a medium mixing bowl, combine the ground beef, egg, almond flour, sea salt, black pepper, garlic powder, and onion powder until just incorporated.
Gently roll the beef mixture into 12 uniform meatballs, being careful not to overwork the meat.
Heat the avocado oil in a large skillet over medium-high heat and sear the meatballs for 2-3 minutes per side until a golden-brown crust forms.
Remove the meatballs from the skillet and set them aside on a plate.
In the same skillet, add the sliced mushrooms and diced onions, sautéing for 5 minutes until the vegetables are tender and caramelized.
Deglaze the pan by pouring in the beef bone broth, using a wooden spoon to scrape up all the flavorful browned bits from the bottom.
Return the meatballs to the skillet, cover with a lid, and simmer on low for 5-7 minutes until the meatballs are cooked through and the sauce has reduced.
Turn off the heat and stir in the Greek yogurt until the sauce is smooth and creamy, then garnish with fresh chopped parsley before serving.