Preheat the oven to 400°F.
In a large mixing bowl, combine the ground beef, French onion soup, breadcrumbs, Parmesan cheese, mozzarella cheese, egg, garlic powder, onion powder, salt, and black pepper. Mix until well combined.
Using your hands, form the mixture into meatballs, about 1 to 1.5 inches in diameter.
Place the meatballs on a baking sheet lined with parchment paper, spacing them about 1 inch apart.
Bake in the preheated oven for 20-25 minutes, or until the meatballs are cooked through and browned on the outside.
If desired, broil for an additional 2-3 minutes for a crispy top.
Remove from the oven and let cool for a few minutes. Garnish with fresh parsley if using, and serve warm.