In a large oven-safe pan brown the ground beef, onion, and garlic. Drain the fat from the mixture. Stir in the tomatoes, salt, and pepper.
While your beef is browning bring a large pot of water to a boil. Once the water comes to a boil add in the cauliflower and cook until it softens about 10 to 15 minutes.
Drain the cauliflower and return it to the pot. Stir in the butter until the butter is completely melted.
Add in the heavy cream, garlic powder, salt, and pepper the cauliflower. Using an immersion blender and blend until smooth and creamy.
If you do not have an immersion blender you can transfer this mixture to a food processor or heavy-duty blender but my favorite to get the right texture is an immersion blender plus I don’t have to dirty extra dishes.
If your pan isn't oven save move the ground beef to an oven-safe casserole dish. Top the beef mixture with the mashed cauliflower, then the cheese.