Heat a large saucepan over medium-high heat. Add beef, onion, and garlic. Cook and stir until beef is browned and crumbly, 5 to 7 minutes. Drain and discard grease. Add mushrooms and cook for 2 to 3 minutes. Stir in basil, oregano, salt, red pepper flakes, fennel, and black pepper.

Pour in diced tomatoes with juice, beef broth, and tomato paste to the saucepan. Mix well. Cover and reduce heat to a simmer. Simmer, stirring occasionally, for 1 hour.