01 - Preheat the oven to 400°F (200°C).
02 - Cook the pasta in salted boiling water according to package directions until al dente. Drain well and set aside.
03 - While the pasta cooks, heat olive oil in a large skillet over medium-high heat. Add diced chicken, season with salt and pepper, and cook until golden and cooked through, about 6–7 minutes. Remove from heat.
04 - In a large bowl, combine cooked pasta, cooked chicken, pesto, cream, milk, half the mozzarella, and cherry tomatoes or spinach if using. Mix thoroughly.
05 - Transfer the mixture into a greased baking dish. Top with remaining mozzarella and Parmesan cheese. Bake for 20 minutes, or until the cheese is bubbly and golden.
06 - Let the dish stand for 5 minutes before serving. Garnish with extra basil if desired.