Place each chicken breast between two pieces of plastic wrap and lightly pound with a meat mallet or rolling pin to approximately 1/4 inch thickness.
Coat a large skillet with nonstick cooking spray. Cook chicken over medium heat for 4-6 minutes or until chicken is no longer pink, turning once to brown evenly. Transfer chicken to patter and keep warm.
In the same skillet, add mushrooms, green onions, water and salt. Cook over medium heat until mushrooms are tender and most of the liquid has evaporated. Add Marsala and heat through. Spoon sauce over chicken and serve.
Serve this dish with whole grain pasta and a side salad for a complete meal.