Preheat oven to 400 degrees. Wash outside of squash if it's dirty then cut the squash in half lengthwise. Be careful, this isn't the easiest thing to do. Scrape out the seeds and stringy stuff.
Drizzle olive over the inside of each squash half and sprinkle with italian seasoning. Line a baking sheet with foil and place the squash open side up on the sheet. Roast for at least 40 min, it may take longer if your squash is large. When it's done, the squash will come apart in strings (like spaghetti) when the inside is scraped.
Meanwhile, shred a rotisserie chicken and set aside. If you are using homemade pesto, make this while the squash is roasting and set aside. Following package directions, cook the frozen vegetables (HIGHLY recommend microwaving as a time saver!).
Spray a 9x13 baking dish with non-stick spray. When the squash is done and cooled slightly (they get HOT, use a hot pad to handle), scrape the inside to make your 'spaghetti'. Scoop into a bowl and gently combine with the shredded rotisserie chicken, pesto, vegetables, parmesan cheese and salt and pepper. Spoon the mixture into the prepared baking dish and spread evenly. Sprinkle with a bit of parmesan cheese. Bake for 20-30 minutes until slightly bubbly. Serve hot!