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.
In a large skillet over medium heat, add the olive oil and sauté the diced yellow onion and minced garlic until they become soft and fragrant.
Add the ground beef to the skillet, breaking it up with a spoon, and cook until it is completely browned.
Stir in the cauliflower rice, tomato puree, sea salt, black pepper, dried oregano, and smoked paprika, allowing the mixture to simmer for 3-5 minutes.
Place the hollowed-out bell peppers upright in a baking dish and fill each one generously with the beef and cauliflower rice mixture.
Pour a small amount of water into the bottom of the baking dish to create steam, then cover the dish tightly with foil.
Bake for 30 minutes, then remove the foil and bake for an additional 5-10 minutes until the peppers are tender and the filling is hot.