Preheat your oven to 375°F (190°C).
Slice the tops off the bell peppers and remove the seeds and membranes.
In a large skillet over medium-high heat, brown the ground beef until fully cooked, then drain any excess fat.
Stir the cooked brown rice, tomato sauce, sea salt, black pepper, garlic powder, and dried oregano into the skillet with the beef.
Simmer the mixture for 2-3 minutes until the flavors are well combined and the sauce has thickened slightly.
Place the hollowed-out bell peppers in a baking dish and fill each one generously with the beef and rice mixture.
Sprinkle the tops with parmesan cheese.
Pour a splash of water into the bottom of the baking dish, cover with foil, and bake for 30 minutes.
Remove the foil and bake for an additional 10 minutes until the peppers are tender and the cheese is golden.