Preheat the oven to 375°F (190°C).
Cut the tops off the bell peppers and remove the seeds and membranes. Rinse the peppers and set aside.
In a large bowl, combine the cooked rice, diced tomatoes, sliced black olives, chopped parsley, olive oil, lemon juice, dried oregano, garlic powder, salt, and pepper. Mix well.
Stuff each bell pepper with the rice mixture and place them in a baking dish.
Cover the baking dish with foil and bake for 40 minutes.
Remove the foil and bake for an additional 10 minutes, or until the peppers are tender and lightly browned.
Serve the stuffed peppers hot and enjoy!