Preheat your oven to 375°F (190°C).
Slice the tops off the bell peppers, remove the seeds and membranes, and set the peppers upright in a small baking dish.
Heat the avocado oil in a skillet over medium heat and sauté the diced onion and minced garlic until translucent and fragrant.
Add the ground beef to the skillet, seasoning with sea salt, black pepper, and dried oregano, and cook until the meat is fully browned.
Drain any excess fat from the skillet, then stir in the cooked brown rice and half of the tomato puree until well combined.
Spoon the beef and rice mixture into the hollowed-out bell peppers, pressing down gently to pack the filling.
Pour the remaining tomato puree over the top of each stuffed pepper.
Cover the baking dish with foil and bake for 30 minutes, then remove the foil and bake for an additional 5-10 minutes until the peppers are tender.
Garnish with chopped fresh parsley before serving.