Preheat the oven to 375°F (190°C).

In a large skillet, heat olive oil over medium heat. Add the chopped onion and minced garlic, sautéing until translucent, about 3-4 minutes.

Add chicken breasts to the skillet. Cook for 6-8 minutes, turning occasionally until golden brown on all sides.

Pour in chicken broth, bring to a simmer. Stir in heavy cream, Dijon mustard, thyme, rosemary, salt, and pepper. Simmer for about 5 minutes.

Stir in shredded cheddar cheese until melted and smooth.

In a mixing bowl, combine cooked rice with the creamy chicken mixture.

Grease a 9x13 inch casserole dish and pour the mixture into it, spreading evenly.

In a bowl, mix breadcrumbs, grated Parmesan cheese, and melted butter. Sprinkle over the casserole.

Bake in the preheated oven for 25-30 minutes until golden brown and bubbling.

Let cool slightly, garnish with fresh parsley, and serve warm.