Place cauliflower in a food processor and pulse into grounds the size of rice grains. Transfer to a large casserole dish.
Combine beef, onion, and garlic in a skillet over medium heat; cook and stir until meat is browned and onion is tender, about 5 minutes. Add green bell peppers and Italian seasoning; continue cooking until slightly tender, about 2 minutes.
Drain excess moisture from the beef mixture. Add tomatoes and beef broth. Simmer until flavors combine, about 5 minutes. Add mixture to the cauliflower in the casserole dish; mix to combine. Shake coconut aminos over the casserole; top evenly with Cheddar cheese.
Bake in the preheated oven until sauce is bubbly, about 35 minutes.