1. In a large bowl, mix together ground beef, almond flour, egg, mushroom, tomato paste, coconut aminos, brown mustard, onion powder, garlic powder, salt and pepper.
2. Form the mixture into balls (about 1 1/2 inch each). Heat olive oil in a skilet over medium-high heat.
3. Brown the meatballs on all sides than transfer to a plate (they will finish cooking in a later step).
4. Prepare the sauce. Heat olive oil in a skillet over medium-high heat. Add onions and cook for about 7 minutes (until translucent). Add garlic and cook for another minute.
5. Add mushrooms, coconut aminos and half of the chicken broth. Stir.
6. Mix the rest of the broth with arrowroot starch, add to the skillet and stir.
7. Add meatballs to the sauce, cover and cook for about 10 minutes, until cooked through. Serve topped with sauce.