Preheat oven to 375°F.
Season chicken breast with a portion of the salt and pepper, bake until cooked through, and shred into bite-sized pieces.
In a skillet, melt ghee over medium heat and sauté onion, carrots, and celery until softened.
Whisk arrowroot powder into cold chicken broth until smooth, then pour into the skillet, stirring until the sauce thickens into a velvety gravy.
Fold in the shredded chicken, peas, thyme, and the remaining salt and pepper.
Transfer the filling mixture to a small oven-safe baking dish.
In a small bowl, mix almond flour with the egg white and a pinch of salt to form a soft dough.
Flatten the dough with your hands and place it over the chicken mixture to cover.
Bake for 20-25 minutes until the crust is golden brown and the filling is bubbling.