Preheat your oven to 375°F (190°C).

Heat olive oil in a large oven-safe skillet or casserole dish over medium heat. Add the chicken pieces and cook until lightly browned on all sides, about 5 minutes. Remove the chicken and set aside.

In the same skillet, add the sliced onions and cook over medium heat, stirring frequently, until caramelized, about 20 minutes. Add the garlic and thyme, cooking for an additional 1 minute.

Stir in the chicken broth, heavy cream, Worcestershire sauce, salt, and pepper, scraping the bottom of the skillet to deglaze and incorporate the caramelized bits.

Return the chicken to the skillet, then stir in the uncooked orzo pasta. Mix well to ensure the orzo is evenly coated and submerged in the liquid.

Sprinkle Gruyère cheese and Parmesan cheese evenly over the top.

In a small bowl, combine the panko breadcrumbs with melted butter. Sprinkle the breadcrumbs over the cheese layer.

Transfer the skillet to the preheated oven and bake for 25-30 minutes, or until the orzo is tender and the top is golden brown and bubbling.

Remove from the oven and let the casserole rest for 5 minutes before serving. Garnish with fresh parsley if desired.