melt butter in a large saucepan over med heat. add onion and saute 3 min. stir in flour, salt,pepper. gradually add milk. stirring until well blended. bring mixture to a simmer and cook 1 minute or until slightly thickened. remove from heat and stir in cooked rice, feta, egg, egg whites and spinach.
pour into a 9 inch pie plate sprayed with sooking spray . sprinnkle with parmesan cheese . bake 400 for 35 minutes or until set