Preheat the oven to 350°F (175°C).
Bring a large pot of salted water to a boil and cook the pasta according to package directions until al dente; drain well.
In a large mixing bowl, combine the drained pasta with pesto, heavy cream (or milk/half-and-half), shredded chicken, frozen peas (no need to thaw), and drained sun-dried tomatoes; stir until evenly coated.
Transfer the pasta mixture to a 9×13-inch baking dish and spread into an even layer; sprinkle the shredded mozzarella evenly over the top.
Bake for 20 minutes, or until the cheese is melted and the casserole is hot throughout.
Remove from the oven and serve immediately.
