Start by bringing a large pot of salted water to a rolling boil over high heat. Add the penne pasta and cook according to package instructions until al dente, usually around 8-10 minutes. Once done, drain the pasta and set it aside, allowing the steam to escape while you prepare the other ingredients.

In a large skillet, heat olive oil over medium heat. Add the diced chicken breast that's seasoned with salt and black pepper. Cook for about 6-8 minutes, stirring occasionally, until the chicken is browned and cooked through. Remove the chicken from the skillet and set it aside on a plate to keep warm.

Using the same skillet, add fresh spinach and sauté for 2-3 minutes, stirring occasionally until wilted. Once wilted, transfer the spinach to the plate with the chicken.

In a large mixing bowl, combine basil pesto with heavy cream. Stir until well blended. Then, fold in the cooked chicken, sautéed spinach, drained penne pasta, and red pepper flakes if desired. Sprinkle in half of the mozzarella cheese, mixing until everything is well coated.

Preheat your oven to 350°F (175°C). Grease a large baking dish to prevent sticking. Pour the creamy pasta mixture into the baking dish, spreading it evenly. Top with the remaining mozzarella cheese and grated Parmesan cheese.

Place the baking dish in the preheated oven and bake for 20-25 minutes, or until the cheese is bubbly and golden brown.

Remove the dish from the oven and let it rest for a few minutes. Garnish with fresh basil leaves before serving.