In a large bowl, combine ground beef, breadcrumbs, Parmesan cheese, parsley, egg, garlic powder, onion powder, salt, and black pepper. Mix until well combined.
Form the mixture into 1.5-inch meatballs.
Heat olive oil in a large skillet over medium heat. Add the meatballs and cook for about 5-7 minutes, turning occasionally, until browned on all sides. Remove meatballs from the skillet and set aside.
In the same skillet, add sliced mushrooms, diced onion, and minced garlic. Sauté for about 5 minutes until the onions are translucent and the mushrooms are tender.
Sprinkle flour over the mixture and stir to combine.
Gradually add beef broth and Worcestershire sauce, stirring constantly to prevent lumps. Add thyme, salt, and pepper.
Bring the mixture to a simmer and cook until slightly thickened, about 3-5 minutes.
Return the meatballs to the skillet, cover, and simmer for an additional 10-15 minutes until the meatballs are cooked through and the flavors meld.
Serve the Salisbury steak meatballs over mashed potatoes or egg noodles.