Preheat the oven to 375°F. Lightly grease a 9×13 inch baking dish.

In a large skillet, heat olive oil and butter over medium heat until melted.

Add the sliced onion and sugar. Cook for 10–12 minutes, stirring frequently, until the onions are golden and caramelized.

Stir in minced garlic and sauté for 1 minute until fragrant.

Push onions to one side of the skillet and add the chicken pieces. Season with salt and pepper. Cook for about 4–5 minutes until lightly browned but not thoroughly cooked.

Stir in orzo, chicken broth, water, and dry French onion soup mix. Bring to a gentle simmer.

Reduce heat and stir in heavy cream, sour cream, half of the shredded Gruyere, and all of the Parmesan. Season with more salt and pepper if needed.

Pour the mixture into the prepared baking dish and spread it evenly. Top with the remaining Gruyere cheese.

Bake uncovered for 20–25 minutes, until the orzo is tender and the cheese is bubbly and golden.

Remove from oven and let it rest for 5 minutes before serving.