01 - Preheat the oven to 400°F.
02 - Cook the pasta in a large pot of salted boiling water until al dente. Drain well and set aside.
03 - Heat olive oil in a large skillet over medium-high heat. Season the diced chicken with salt and pepper, then add to the pan. Cook for 6–7 minutes until golden brown and cooked through. Remove from heat.
04 - In a large mixing bowl, combine the cooked pasta, cooked chicken, basil pesto, heavy cream, milk, half of the mozzarella cheese, and the optional spinach or tomatoes. Stir until evenly coated.
05 - Transfer the pasta mixture into a greased baking dish. Sprinkle the remaining mozzarella and the Parmesan cheese evenly over the top.
06 - Bake for 20 minutes, or until the cheese is bubbly and golden brown.
07 - Let the stand for 5 minutes before serving to set.