Sauté the aromatics: In a large pot, heat olive oil over medium heat. Add diced onions and cook until soft, about 3 minutes. Stir in garlic and cook for another minute.
Brown the beef: Add ground beef to the pot. Season with salt, pepper, Italian seasoning, and red pepper flakes. Cook until fully browned.
Add tomato flavor: Stir in tomato paste and cook for 2 minutes until deepened in color. Add marinara sauce and beef broth, stirring well.
Simmer and add pasta: Bring to a simmer. Add broken lasagna noodles and cook until al dente, about 12–15 minutes, stirring occasionally.
Prepare the cheese mixture: While the soup simmers, mix ricotta, mozzarella, Parmesan, and parsley in a small bowl.
Serve and enjoy: Ladle soup into bowls and top with a generous dollop of the cheese mixture. Sprinkle more mozzarella and parsley on top if desired.