Preheat oven to 375°. In a large skillet, cook chicken and onion over medium-high heat 7-9 minutes or until chicken is no longer pink, breaking up meat into crumbles; drain. Stir in seasonings. Add spinach; cook and stir until liquid is evaporated. Transfer to a large bowl; cool slightly. Stir in beaten eggs and cheese.
Layer 10 sheets of phyllo dough in a greased 13x9-in. baking dish, spritzing each with cooking spray. (Keep the remaining phyllo covered with a damp towel to prevent it from drying out.) Spread spinach mixture over phyllo. Top with remaining sheets of phyllo, spritzing each with cooking spray. Cut into 8 rectangles.
Bake, uncovered, 35-40 minutes or until golden brown. If necessary, recut rectangles before serving.