Set your oven to 350°F (175°C) to preheat.
Cook the ground beef in a skillet over medium heat until browned.
Remove excess fat, then stir in marinara sauce, Italian seasoning, salt, and black pepper.
Add cauliflower rice and half of the mozzarella cheese, mixing well.
Transfer the mixture into a baking dish evenly.
Sprinkle the rest of the mozzarella cheese on top, then layer with pepperoni slices.
Bake for 25 to 30 minutes until the cheese melts and turns golden.
Allow the casserole to sit for a couple of minutes before serving.