Preheat the oven to 375°F (190°C). Lightly grease a 9x13-inch baking dish.
Steam or microwave the cauliflower florets until just tender, about 5–7 minutes. Drain well and set aside.
In a large skillet over medium heat, cook the ground beef and onion until the beef is browned. Drain excess grease.
Add the garlic, tomato soup, sour cream, Italian seasoning, salt, and black pepper. Stir until combined.
Spread the cooked cauliflower evenly in the prepared baking dish.
Pour the beef mixture over the cauliflower and stir gently.
Sprinkle the shredded cheddar cheese evenly on top.
Bake uncovered for 25–30 minutes, until hot and bubbly and the cheese is melted.
Garnish with parsley, if desired, and serve warm.