Preheat your oven to 375°F (190°C).
Slice the tops off the bell peppers and carefully remove the seeds and membranes from the inside.
Heat the olive oil in a large skillet over medium heat, then add the diced onion and minced garlic, sautéing until fragrant and translucent.
Add the ground beef to the skillet, breaking it apart with a spoon, and cook until it is fully browned. Drain any excess liquid from the pan.
Stir in the cooked brown rice, tomato puree, sea salt, black pepper, dried oregano, and smoked paprika, allowing the mixture to simmer for 2 minutes.
Spoon the beef and rice mixture into the prepared bell peppers, packing it down gently.
Place the stuffed peppers upright in a baking dish and add a small splash of water to the bottom of the dish to create steam.
Cover the dish tightly with foil and bake for 30 minutes.
Remove the foil and continue baking for another 10 minutes until the peppers are tender and the tops are slightly golden.