Bring a large pot of salted water to a boil and cook the penne pasta according to package instructions until al dente. Drain well and set aside to cool slightly. Cooking the pasta just right ensures it won’t become mushy after baking.
In a large mixing bowl, whisk together the heavy cream, grated Parmesan cheese, pesto sauce, garlic powder, salt, and black pepper until smooth and creamy. This mixture is the heart of the casserole’s rich flavor profile.
Add the shredded cooked chicken and cooked penne pasta to the bowl with the sauce. Stir gently but thoroughly so every piece of pasta and chicken is coated with the creamy pesto Alfredo mixture.
Transfer the mixture into a greased 9x9-inch baking dish and spread it evenly. Scatter the halved cherry tomatoes on top, then sprinkle the shredded mozzarella cheese over everything to create that irresistible cheesy crust.
Preheat your oven to 350°F (175°C) and bake the casserole uncovered for 20-25 minutes. You want the cheese melted and bubbly with a golden hue, and the casserole warmed through.
Let the casserole cool for a few minutes before serving. This allows the sauce to set slightly, making it easier to scoop out perfect portions. Pair with a simple green salad or garlic bread for a full meal.