Preheat your oven to 375°F (190°C).

Heat olive oil in a large oven-safe skillet over medium-high heat.

Season the chicken breasts with salt and pepper, then sear them in the skillet for 4-5 minutes per side until golden brown. Remove the chicken and set aside.

Reduce the heat to medium and melt the butter in the skillet. Add the sliced onions and cook, stirring occasionally, for 15-20 minutes until they are caramelized and golden brown.

Stir in the dried thyme and deglaze the skillet with white wine (if using), cooking for 1-2 minutes until the liquid has mostly evaporated.

Add the chicken broth, heavy cream, and garlic powder to the skillet, stirring to combine.

Mix in the uncooked orzo pasta and bring the mixture to a simmer.

Return the chicken breasts to the skillet, nestling them into the orzo mixture.

Sprinkle the Gruyère and Parmesan cheeses evenly over the top.

Transfer the skillet to the preheated oven and bake for 20-25 minutes, or until the orzo is tender, the chicken is cooked through, and the cheese is melted and bubbly.

Remove the skillet from the oven and let it rest for 5 minutes. Garnish with chopped parsley, if desired, before serving.