Heat a large skillet over medium-high heat. Cook and stir beef and onion in the hot skillet until beef is browned and crumbly, 5 to 7 minutes; drain and discard grease.

Stir beef-onion mixture, beef broth, marinara sauce, pepperoni, Parmesan cheese, garlic, minced onion, and oregano together in a large pot; bring to a boil, reduce heat to low, and simmer until flavors blend, about 20 minutes.

While soup is simmering, bring a pot of lightly salted water to a boil. Cook the ravioli at a boil, stirring occasionally, until cooked through yet firm to the bite, about 14 minutes; drain.

Stir ravioli into soup and cook until heated through, 3 to 5 minutes. Ladle soup into bowls and top with mozzarella cheese.