Preheat your oven to 375°F (190°C).
In a large baking dish, combine the uncooked rice, chicken broth, lemon juice, oregano, salt, and pepper. Stir it up.
Add the diced chicken evenly across the top—don’t stir it in.
Spoon dollops of tzatziki across the chicken. Let it hang out like that.
Top it all with grape tomatoes and sliced onion.
Cover the dish tightly with foil and bake for 35-40 minutes, or until the rice is cooked and the chicken is done.
Remove the foil and let it cool for 5 minutes. Garnish with parsley if you're feeling fancy, and serve with extra tzatziki on the side.