Carefully slice each croissant horizontally, almost all the way through, like you're making a sandwich. Set them aside.

Melt the butter in a large skillet over medium heat. Add the sliced mushrooms and cook, stirring occasionally, until they're softened and browned, about 5-7 minutes.

Sprinkle the flour over the cooked mushrooms and stir constantly for about a minute.

Gradually pour in the chicken broth and milk, stirring continuously to prevent lumps from forming. Keep stirring until the sauce begins to thicken, which should take about 2-3 minutes.

Add the softened cream cheese, garlic powder, onion powder, thyme, salt, and pepper to the sauce. Stir until the cream cheese is fully melted and incorporated, and the sauce is smooth and creamy.

Add the shredded or diced cooked chicken to the sauce. Stir well to combine everything evenly.

Carefully spoon the chicken and mushroom mixture into each sliced croissant.

Place the filled croissants on a baking sheet lined with parchment paper. Bake in a preheated oven at 375°F (190°C) for 10-12 minutes, or until the croissants are golden brown and heated through.

Remove the croissants from the oven and let them cool slightly. If desired, sprinkle with fresh chopped parsley before serving.