Cook the orzo pasta according to package instructions, drain, and set aside.
In a large skillet, heat olive oil over medium heat. Add diced chicken, season with salt, pepper, and garlic powder. Cook for 5-7 minutes until no longer pink. Remove from skillet.
In the same skillet, add sliced onions and cook over medium heat for 10-15 minutes until golden brown and caramelized.
In a large mixing bowl, combine cooked orzo, sautéed chicken, caramelized onions, French onion soup, and dried thyme. Mix well.
Preheat oven to 375°F. Transfer mixture to a greased 9x13-inch baking dish, spread evenly, and top with mozzarella and cheddar cheese. Cover with foil and bake for 25 minutes, then remove foil and bake for an additional 10-15 minutes until cheese is bubbly and golden.
Let cool for a few minutes before serving. Garnish with fresh parsley.