In a medium bowl, mix the ground beef with the egg, garlic powder, onion powder, salt, and pepper until just combined.
Roll the beef mixture into small, uniform meatballs, roughly 1 inch in diameter.
Heat the olive oil in a large non-stick skillet over medium heat and add the meatballs.
Sear the meatballs for 8-10 minutes, turning occasionally until browned on all sides and cooked through.
Remove the meatballs from the skillet and set aside on a plate.
Add the sliced cremini mushrooms to the same skillet, sautéing for 5 minutes until they release their moisture and turn golden brown.
In a small jar, shake the beef bone broth and arrowroot powder together until no lumps remain.
Pour the broth mixture into the skillet with the mushrooms, stirring frequently as the sauce bubbles and thickens into a glossy gravy.
Return the meatballs to the skillet, tossing gently to coat every piece in the mushroom sauce.
Garnish with chopped fresh parsley and serve immediately.