Preheat oven to 350F. Coat a baking dish with nonstick cooking spray. Sprinkle both sides of chicken with seasoning, and black pepper to taste; place in baking dish. Bake 20 minutes or until an instant-read thermometer registers 165F.
Meanwhile, for the dressing, in a small bowl combine lemon juice, lemon zest, mustard and oil. In a large bowl combine greens and onion. Drizzle greens with dressing; toss lightly to coat.
Place salad on 4 serving plates. Cut or shred each chicken breast into pieces and place on top of each salad. Top evenly with shaved Parmesan, and serve.