Preheat oven to 350°. Cook rice, either on the stove or in the microwave. To cook on the stove: Bring 2 cups water to a boil, add 1 teaspoon olive oil, then stir in rice. Reduce heat and simmer covered for 7-8 minutes, or until tender. To cook in the microwave: Combine 2¼ cups water, 1 tablespoon olive oil, and rice in a 2-quart microwave-safe bowl. Microwave uncovered for 10-12 minutes, or until rice is tender.
Heat 3 tablespoons olive oil in a large skillet over medium-high heat. Add protein, season with salt, pepper, and oregano, and cook for 8-10 minutes or until browned. Remove from heat, drain excess oil, and transfer protein to a large mixing bowl.
Wipe the skillet clean, add remaining olive oil, and sauté onions until browned.
Add to the mixing bowl with the protein. Then, combine cooked rice, drained diced tomatoes, and tomato sauce with the protein and onions.
To assemble, spoon half the mixture into the peppers, layer with half the pack of cheese, then fill peppers with the remaining mixture.
Cover peppers with foil and bake for 30 minutes. Remove foil, top with remaining cheese, and return to the oven for an additional 15-20 minutes, or until the cheese is melted and lightly browned.