In a medium bowl, combine seasoning mix and chicken and stir to coat.
In a large skillet, heat oil over medium-high until shimmering. Add chicken and cook for 5 to 7 minutes, stirring frequently, until no longer pink. Remove the pan from the heat and set aside.
Unroll one of the tubes of crescent rolls into a buttered 13x9x2-inch baking dish. Firmly pinch together perforations and press the dough to fit bottom of the dish. Place layer of cheese over the dough to cover. With a slotted spoon, Spread the chicken over the dough and top with the spinach.
In a medium bowl, beat 3 eggs, Parmesan cheese, and pepper, together until well blended. Pour this mixture over the spinach. Unroll the remaining dough and press into place on top of the spinach.
In a small bowl, beat the egg yolk together with the milk. Brush the top of the dough with the yolk mixture. Bake covered for 30 minutes. Remove the cover and bake for another 10 minutes or until the pastry is golden. Let stand for 10 minutes before cutting into squares.