Preheat the oven to 375°F (190°C).
In a large skillet, heat olive oil over medium heat.
Add the sliced onions to the skillet and cook until caramelized, about 20 minutes, stirring frequently.
Once the onions are caramelized, add the diced chicken and thyme to the skillet, cooking until the chicken is no longer pink.
In a large bowl, mix the orzo, chicken broth, sour cream, half of the cheese, and the seasoned chicken and onions.
Transfer the mixture to a greased baking dish and top with the remaining cheese.
Bake for 25-30 minutes, or until the cheese is golden brown and bubbly.
Remove from the oven and let rest for 5-10 minutes before serving.