Lightly rub the inside and outside of the peppers with olive oil and place them upside down in a baking dish or on a sheet pan.
Roast for 20-25 minutes, depending on how soft you like your stuffed peppers. (These should be removed from the oven and set aside when done, but move onto the filling steps while they’re roasting.)
Saute the garlic and onion in olive oil until beginning to turn fragrant, then add the cauliflower rice. Mix and cook until any excess moisture is removed from the cauliflower rice.
Add ground beef, salt, pepper, and Italian seasoning to skillet, mix, and saute until the beef is browned.
Remove skillet from heat and mix in tomato sauce and 3/4 cup Mozzarella cheese.
Flip peppers over and stuff with the stuffing mixture. Sprinkle tops with remaining 3/4 cup Mozzarella cheese.
Return to the oven and bake for 15-20 minutes until cheese has melted and the stuffing is fully heated.
Notes
I didn’t do it for these photos, but for that special extra-gooey melted cheese look, shred your Mozzarella cheese by hand. Pre-shredded cheese contains anti-caking agents that make it difficult to melt.