Bring a large pot of salted water to a boil and cook the pasta according to package directions until al dente; reserve 1/2 cup pasta water, then drain and set aside.
Heat 2 tablespoons olive oil in a 12" skillet over medium heat. Add the chicken pieces, season with salt, pepper, and 1 teaspoon Italian seasoning, and cook 5–7 minutes until cooked through and golden, stirring occasionally; transfer chicken to a plate.
Reduce heat to low and add the pesto and heavy cream (if using) to the same skillet; warm, stirring until combined.
Add the minced garlic and cook 1 minute more until fragrant, then stir in 2 tablespoons grated Parmesan and 1/4 teaspoon red pepper flakes (if using).
Return the cooked chicken and drained pasta to the skillet and toss to coat; if the sauce is too thick, add reserved pasta water a tablespoon at a time until desired consistency is reached.
Divide among plates and top with toasted pine nuts, fresh basil leaves, and extra grated Parmesan before serving.
