Preheat the oven to 375 degrees. Spray a 9x13 baking dish with nonstick spray.
Cut peppers in half lengthwise, remove seeds, and place in the baking dish, cut side up.
Cook the ground beef in a nonstick skillet over medium heat until brown, about 7 minutes. Drain meat and set aside.
Place the skillet back on medium heat. Add the olive oil and onion. Cook onions until tender, about 5 minutes, stirring occasionally. Add the minced garlic and cook another minute, taking care not to burn the garlic.
Add the tomatoes, Italian seasoning, salt, pepper and red pepper flakes. Reduce heat to medium low. Bring to a simmer and cook for about 3 minutes until the tomatoes are warmed.
Add the cooked meat and cauliflower rice. Stir together. Cook another 2-3 minutes until warmed through.
Remove the pan from the heat. Add half of the cheese. Stir together until the cheese melts.
Divide the filling into the cut pepper halves. It’s ok if it’s overfilled, they won’t spill during baking. Top with the remaining cheese.
Spray a sheet of aluminum foil and place it over the stuffed peppers, sprayed side down. This will keep the cheese from sticking to the foil.
Bake in a preheated oven for 30 minutes, then remove the foil and bake another 15 minutes or until the peppers are fork tender.