Place chicken in a zip-lock bag and pour 1 cup of balsamic vinaigrette in bag with chicken. Marinate for 2 hours or more- best marinated overnight.
In a grill pan, grill chicken breasts, about 5 to 6 minutes on each side. Cook thoroughly. Once cooled, dice chicken up in small bites.
Whisk together ½ cup balsamic vinaigrette dressing and mustard in a small bowl.
Cook pasta according to package directions; drain. Transfer pasta to a large bowl and drizzle with 1/2 tablespoon olive oil. Let cool 10 minutes.
Toss together pasta, chicken, balsamic mixture, spinach, and remaining 3 ingredients in a large bowl. Serve immediately, or, if desired, cover and chill 1 hour before serving
