Preheat your oven to 375°F.
Slice the tops off the bell peppers and carefully remove the seeds and inner membranes.
In a large skillet over medium heat, sauté the diced onion and minced garlic until they become soft and translucent.
Add the ground beef to the skillet, breaking it into small crumbles with a wooden spoon, and cook until it is fully browned.
Stir in the cooked brown rice, tomato puree, dried oregano, sea salt, and black pepper.
Simmer the beef and rice mixture for about 5 minutes until the sauce has thickened and the flavors are well combined.
Remove the skillet from the heat and stir in the Greek yogurt to create a creamy, protein-packed binder for the filling.
Stuff each bell pepper cavity tightly with the beef and rice mixture.
Place the stuffed peppers upright in a baking dish and pour 0.25 cup of water into the bottom of the dish to create steam.
Cover the dish tightly with foil and 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.