Preheat the Oven: Preheat your oven to 375°F (190°C). Lightly grease a 9×13-inch baking dish and set aside.

Cook the Pasta: Cook the penne rigate according to the package instructions until al dente. Drain and set aside.

Prepare the Sauce: In a large mixing bowl, combine the sour cream, cream cheese, milk, and dry ranch seasoning mix. Use a hand mixer or whisk to blend until smooth and creamy.

Add Spinach and Chicken: Fold in the thawed and squeezed spinach, followed by the shredded chicken. Mix until evenly distributed.

Combine Pasta and Sauce: Add the cooked penne pasta to the sauce mixture. Gently toss until the pasta is fully coated.

Layer in the Baking Dish: Transfer the pasta mixture to the prepared baking dish. Spread it out evenly.

Add Cheese Topping: Sprinkle the shredded mozzarella cheese evenly over the top of the pasta.

Bake: Place the dish in the preheated oven and bake for 20-25 minutes, or until the cheese is melted and bubbly, and the edges are lightly golden.

Broil (Optional): For an extra golden top, switch the oven to broil for the last 2-3 minutes, keeping a close eye to prevent burning.

Cool and Serve: Remove from the oven and let it cool for 5 minutes before serving.