Preheat oven to 400°F (200°C) and lightly grease a 9x13 inch baking dish.
Add the uncooked pasta, cubed chicken, chicken broth, minced garlic, dried oregano, salt, and pepper directly into the baking dish.
Stir the ingredients to ensure the pasta is evenly distributed and mostly submerged in the liquid.
Cover the dish tightly with aluminum foil to prevent steam from escaping.
Bake for 35 to 40 minutes, or until the pasta is tender and the chicken reaches an internal temperature of 165°F (74°C).
Remove from the oven and carefully uncover.
Stir in the tzatziki sauce and lemon juice until the mixture is creamy and well combined.
Top the casserole with diced cucumber, crumbled feta, and fresh dill before serving.