Preheat oven to 375 degrees. Coat a 3 quart rectangular baking dish with cooking spray.
In an extra-large skillet, heat butter over high heat until melted. Add ground chicken and onion; cook about 8 minutes or until chicken is browned and onion is tender, breaking up chicken as it cooks. Drain off fat. Stir in spinach, 1 teaspoons freshly ground black pepper, 1/2 teaspoons salt, the nutmeg and crushed red pepper; cook and stir for 5 minutes. Transfer mixture to a bowl. Stir in eggs, cheese, and oregano.
Unfold phyllo dough. Cut a 1" strip off one of the short ends of the phyllo stack; discard. Place a phyllo sheet in the bottom of the prepared baking dish; lightly coat with cooking spray. As you work, cover the remaining phyllo with plastic wrap to prevent it from drying out. Top with seven more phyllo sheets, coating each sheet with cooking spray. Spread chicken mixture over phyllo in dish. Top with the remaining phyllo, coating each sheet with cooking spray.
Bake, uncovered, about 45 minutes or until mixture is heated through and phyllo is golden.