Preheat your oven to 375°F (190°C) and lightly grease a small baking dish.
Slice the tops off the bell peppers and remove the seeds and membranes from the inside.
Heat the olive oil in a skillet over medium heat, then sauté the diced yellow onion and minced garlic until fragrant and translucent.
Add the ground beef to the skillet, breaking it apart with a wooden spoon, and cook until fully browned.
Stir in the cooked brown rice, tomato puree, sea salt, black pepper, and smoked paprika until the mixture is well combined and heated through.
Spoon the beef and rice mixture into the hollowed bell peppers, pressing down gently to ensure they are well packed.
Place the peppers upright in the baking dish, add a small splash of water to the bottom of the dish, and cover tightly with foil.
Bake for 30 minutes, then remove the foil and bake for an additional 10 minutes until the peppers are tender and the tops are slightly golden.
Garnish with chopped fresh parsley before serving hot.