Preheat your oven to 375°F (190°C).
In a large skillet, heat the olive oil over medium heat. Add the diced chicken, garlic powder, onion powder, oregano, salt, and pepper. Cook until the chicken is browned and cooked through, about 5-7 minutes.
In a mixing bowl, combine the Greek yogurt, diced cucumber, lemon juice, and dill. Stir until well mixed.
In a large baking dish, layer the cooked rice evenly on the bottom. Top with the cooked chicken mixture, spreading it out evenly.
Spoon the tzatziki mixture over the chicken, spreading it to cover the surface.
Sprinkle the shredded mozzarella cheese on top, followed by the cherry tomatoes and olives if using.
Bake in the preheated oven for 25-30 minutes, or until the cheese is melted and bubbly.
Remove from the oven and let it cool for a few minutes before serving.