Combine first 3 ingredients in a saucepan over medium-high heat. Bring mixture to a simmer; cover and cook for 2 hours, 15 minutes or until wheat berries are almost tender. Drain and place in a bowl; discard bay leaf. Coarsely chop 1 cup spinach leaves. Add chopped spinach, apple, bell pepper, dressing, and mustard to the wheat berries, and toss well.
Sprinkle chicken with salt and pepper. Place chicken on a grill rack coated with cooking spray; grill 5 minutes on each side or until done. Thinly slice chicken.
Divide remaining spinach evenly among 4 plates. Place 1/2 cup wheat-berry mixture on top of spinach. Arrange chicken evenly over berry mixture; sprinkle with green onions.