Preheat oven to 375°F (190°C).
In a 9x13-inch baking dish, combine the rinsed white rice, chicken broth, olive oil, dried oregano, garlic powder, salt, and black pepper. Stir to distribute seasonings.
Distribute the cubed chicken breast evenly across the surface of the rice and liquid mixture.
Seal the baking dish tightly with heavy-duty aluminum foil to ensure steam is retained.
Bake for 40 to 45 minutes until the internal temperature of the chicken reaches 165°F (74°C) and the rice has absorbed the liquid.
Prepare the tzatziki garnish by whisking together the Greek yogurt, squeezed cucumber, lemon juice, and minced dill in a small mixing bowl.
Remove the baking dish from the oven and allow it to rest, covered, for 5 minutes.
Remove the foil and fluff the rice using a fork to integrate the chicken.
Top the rice and chicken with dollops of the prepared tzatziki, halved cherry tomatoes, and sliced Kalamata olives immediately before serving.