Begin by bringing a large pot of salted water to a boil. Once boiling, add your choice of pasta and cook according to package instructions until al dente, usually around 8-10 minutes. After draining, rinse the pasta under cool water to halt the cooking process and prevent mushiness, then set aside.

In a spacious mixing bowl, combine the shredded rotisserie chicken, cream of chicken soup, and sour cream, stirring until smooth and well-integrated. Next, add the fresh chopped spinach, half of the grated Monterey Jack cheese, and minced garlic. Mix everything thoroughly until the ingredients are evenly coated.

Gently fold the cooked pasta into the chicken mixture, ensuring that the pasta is evenly distributed and coated with the luscious creamy sauce.

Preheat your oven to 350°F (175°C) to prepare for baking. While it warms up, spray a 9x13-inch baking dish with non-stick cooking spray to prevent sticking. Pour the chicken and pasta mixture into the prepared baking dish.

Sprinkle the remaining grated Monterey Jack cheese evenly over the top of the casserole, followed by the French fried onions.

Place the assembled casserole in your preheated oven and bake for 40-45 minutes, or until the top is golden brown and bubbly.