Preheat oven to 350°F.
Add the olive oil to a large skillet over medium high heat.
Add the ground beef, cauliflower rice, and garlic. Season with salt and pepper.
Cook, stirring occasionally, until the beef is brown and no longer pink, about 5-7 minutes.
While the beef and cauliflower are cooking, mix together the tomato sauce and Italian seasoning in a bowl.
Add half of the sauce to the ground beef and cauliflower. Mix thoroughly.
Spoon the beef mixture evenly into the prepared peppers and place upright in a casserole dish.
Pour the remaining sauce over the tops of the stuffed peppers.
Cover and bake, basting occasionally, until the peppers are tender - about an hour.
Uncover and top evenly with the mozzarella cheese. Bake an additional 3-5 minutes until the cheese is melted and browned (you can also use the broiler for 1-2 minutes, watching closely).