In a skillet, heat the olive oil in medium to high heat. When the oil is hot add the garlic and onion and sauté until golden.
Add the ground beef along with oregano, salt, pepper and tomatoes and stir well for five minutes.
Add 2 cups of water and let it cook for 15 minutes in medium heat. Once the water is absorbed remove from heat, add the yogurt and mix well.
Meanwhile remove the stems from the peppers leaving a small part attached to the pepper to use as lid.
Stuff the peppers with the mix and place them in tray. Any remaining mix you can place it between the peppers.
Add two cups of water in the tray. Cook the peppers for 1 hour at 400F. For the first 40 minutes cover the tray with aluminum foil and then remove it for the last 20 minutes.