In a large pot or Dutch oven, heat over medium heat. Add the ground beef, breaking it up with a wooden spoon. Cook until browned, about 5-7 minutes. Drain any excess fat.
Add the diced onion and minced garlic to the pot. Sauté until the onion is translucent, about 3-4 minutes.
Stir in the diced green, red, and yellow bell peppers. Cook for another 3-5 minutes until the peppers are tender.
Pour in the diced tomatoes with their juices and the beef broth. Add the Italian seasoning, salt, and pepper. Stir well to combine.
Bring the soup to a boil, then reduce the heat to low. Add the cauliflower rice and let simmer for 10-15 minutes, allowing the flavors to meld and the cauliflower to cook.
Taste and adjust seasoning if necessary. Serve hot, garnished with shredded cheese and fresh parsley if desired.