Heat grill to medium-high heat or oven to 350 degrees F. Cut foil into four 12" x 18" pieces and spray each with cooking spray.
Season both sides the chicken breast halves with salt and pepper. Place a chicken breast onto the center of each piece of foil. Spoon 1/4 cup marinara sauce over the top of each breast. Lay zucchini slices over top and sprinkle with Parmesan cheese.
Fold two sides of the foil up and bring together. Fold over twice, leaving room for circulation. Fold over the other two ends of the foil to seal.
Grill for 15 to 20 minutes or bake for 30 minutes, until chicken reaches an internal temp of 170 degrees F in the thickest part.
While chicken is cooking, bring a large pot of lightly salted water to a boil and cook spaghetti according to package directions. Drain and return pasta to pot. Toss with the remaining one cup marinara sauce and cook until heated through.
Cut a slit in each packet to let out steam. Remove chicken from packets and serve over top the spaghetti marinara. Sprinkle with the mozzarella cheese and parsley. Enjoy!