Preheat your oven to 375°F and line a baking dish with parchment paper for easy cleanup.
Slice the bell peppers in half lengthwise, carefully removing the seeds and white membranes to create a clean cavity.
In a large skillet over medium heat, warm the olive oil and sauté the diced onion until it becomes translucent and fragrant.
Add the lean ground beef to the skillet, using a wooden spoon to break it into small crumbles as it browns completely.
Incorporate the cauliflower rice, tomato sauce, garlic powder, dried oregano, sea salt, and black pepper, simmering for 5 minutes to meld the flavors.
Arrange the pepper halves in the prepared baking dish and spoon the beef mixture into each half, pressing down gently to fill.
Cover the dish tightly with foil and bake for 30 minutes, then remove the foil and bake for another 5 minutes until the peppers are tender.
Finish with a sprinkle of fresh chopped parsley for a burst of color and brightness before serving.