Preheat your oven to 400 degrees F and spray a large baking dish with a non-stick spray. Set aside.
Bring a large pot of salted water to a rolling boil. Add the pasta, and cook for 5 minutes ONLY. Drain and set aside.
To a large bowl, combine the partially cooked pasta, chicken, onion, garlic and a heavy dose of salt and black pepper. Toss. Set aside.
In a small saucepan, combine the soup and milk. Whisk over low heat until heated though and creamy. Pour the sauce over the pasta mixture and drizzle on the lemon juice. Stir to evenly coat.
Pour the mixture into your prepared baking dish, cover with foil and bake for 1 hour. After it has baked, remove the foil, and sprinkle the parmesan cheese on top. Place the dish under the broiler until the cheese is melty. Remove from heat.
Garnish with fresh parsley and slices of lemon. Enjoy hot.