Bring a large pot of salted water to a boil. Add the penne pasta and cook according to package instructions until al dente. Drain the pasta and set it aside.
While the pasta cooks, heat olive oil in a large skillet over medium-high heat. Season the chicken breasts with Italian seasoning, salt, and pepper. Cook for 5-6 minutes per side until golden brown and cooked through. Remove from heat, let rest, then slice into bite-sized pieces.
In a large mixing bowl, combine the cooked penne pasta, sliced chicken, and pesto sauce. Toss until well coated.
Preheat oven to 375°F (190°C). Transfer half of the pasta mixture into a baking dish. Evenly distribute half of the cherry tomatoes and mozzarella balls over the pasta. Add the remaining pasta mixture on top, then layer the rest of the tomatoes and mozzarella. Sprinkle grated Parmesan cheese evenly over the top.
Bake for 20-25 minutes until the cheese is melted, bubbly, and lightly golden on top.
Remove from oven and let cool slightly. Garnish with fresh basil leaves before serving.