Prepare the chicken by dicing it into bite-sized pieces and seasoning with garlic powder, dried thyme, salt, and black pepper.
Cook the orzo in a pot of salted boiling water according to package instructions, usually about 8-10, then drain.
Sauté the sliced onions in olive oil over medium heat until caramelized and golden brown, about 15-20.
Combine the cooked orzo, sautéed onions, seasoned chicken, condensed French onion soup, and sour cream in a large mixing bowl. Mix well and fold in half of the shredded cheeses.
Transfer the mixture to a greased 9x13 inch baking dish, top with remaining cheeses, and bake in a preheated oven at 350°F for 25-30 until bubbly and golden brown.