Combine all ingredients for marinade except chicken breasts in a gallon size plastic bag. Add the chicken breasts and let marinade in the fridge for at least 6 hours or over night.
When chicken is done marinating, grill or bake in oven preheated to 400 degrees for about 25 minutes. Chop into 1/2 inch x 1 inch strips and set aside.
Cook spaghetti according to package directions. Strain and set aside.
While the spaghetti is cooking, prepare the gravy by adding the butter to a saute pan over medium heat. Add the garlic and saute until fragrant. Whisk in the flour and cook for about two minutes while continuing to whisk. Add the chicken stock and simmer until the gravy is thick.
Toss the spaghetti with the chicken, diced tomatoes, chopped parsley, parmesan, and garlic gravy until well coated. Serve and top with additional parmesan.