Place each chicken breast half between two sheets of heavy plastic wrap. Pound with the flat side of a meat mallet until 1/8" thick. Season with salt and pepper. Set aside. In a large skillet, cook spinach and onion in hot oil until onion is tender. Remove from heat. Stir in cream cheese until blended. Stir in remaining cheese, egg yolk, flour, nutmeg and cumin. Place about 1/4 cup of the spinach mixture on each chicken breast half. Roll up jelly-roll stlyle. Not necessary to seal ends. Place one sheet of phyllo on work surface. Keep rest of sheets covered with a damp towel. Brish with some of the melted margarine or butter. Place another phyllo sheet on top of the first. Brush with margarine. Place one chicken roll near the short side of the phyllo. Roll chicken and phyllo over once to cover chicken. Fold in long sides, continue rolling from short side. Place in a shallow baking pan. Repeat with rest of chicken, phyllo and margarine. Brush with margarine. Bake, uncovered in a 350 F. oven for 30-35 minutes or until chicken is no longer pink. Serving Ideas : A very elegant entree. NOTES : Submitted by Carol Nerlino, Venice, FL Per serving: 541 cals., 33 g. fat, 150 mg. chol.