1Spray 12-inch skillet with cooking spray; heat over medium heat. Cook chicken in skillet 2 minutes on each side; reduce heat to medium-low. Stir in milk, broth and onion. Cook about 5 minutes, turning chicken occasionally, until onion is tender.
2Stir in spinach. Cook 3 to 4 minutes, stirring occasionally, until spinach is completely wilted and juice of chicken is no longer pink when center of thickest part is cut (170°F). Remove chicken from skillet; keep warm.
3Increase heat to medium. Cook spinach mixture about 3 minutes or until liquid has almost evaporated. Stir in salt, pepper and nutmeg. Serve chicken on spinach.