Preheat your oven to 400°F (200°C) and grease a 9x13-inch baking dish with olive oil or butter.

In a large pot, bring salted water to a boil and add the pasta, cooking for 2 minutes less than the package suggests.

Heat a tablespoon of olive oil in a large skillet over medium heat. Season the chicken and sauté for 5-6 minutes.

In the same skillet, melt 2 tablespoons of unsalted butter over medium heat, add minced garlic, sauté for 30 seconds.

Slowly pour in heavy cream and whole milk, simmer for 2-3 minutes, then stir in the basil pesto and grated Parmesan.

In a large mixing bowl, combine the cooked pasta and sliced chicken with the creamy pesto sauce, folding in baby spinach if using.

Transfer the mixture into the greased baking dish, top with shredded mozzarella and extra Parmesan.

Bake uncovered for 20-25 minutes until the cheese is golden and bubbly.

Let it rest for 5 minutes before serving.