1. Bring broth, water, and Italian seasoning to a simmer in saucepan.
2. Sprinkle chicken with salt and pepper. Heat 1 tablespoon oil in 12-inch nonstick skillet over high heat. Add chicken and cook 1-1/2 minutes per side, until browned. Transfer with slotted spoon to bowl.
3. Add remaining 1 tablespoon oil to skillet. Add mushrooms; cover and cook 2 minutes until softened. Add orzo and cook 1 minute, until lightly toasted. Set 1 cup hot broth aside in glass measure. Gradually add remaining broth to pasta, 1 cup at a time, every 2 to 3 minutes, stirring occasionally. (Mixture will be soupy, but that's okay.) Add chicken and reserved 1 cup broth and cook 2 to 4 minutes more, until thickened. Stir in Parmesan.