Start by bringing a large pot of salted water to a boil. Add 8 ounces of your choice of penne or fusilli pasta and cook according to package instructions until al dente. Drain the pasta, reserving about 1/4 cup of the pasta water, and set aside.
Heat 1 tablespoon of olive oil over medium-high heat in a large skillet. Add the diced chicken breasts and season with salt and pepper. Cook until the chicken is golden brown on all sides and cooked through, about 6-8 minutes. Remove the chicken from the skillet and set aside.
Reduce the heat to medium. In the same skillet, add the minced garlic and red pepper flakes (if using). Sauté for about 1 minute until fragrant, being careful not to burn the garlic.
Stir in the sliced sun-dried tomatoes and chopped spinach. Cook for 2-3 minutes until the spinach wilts and the tomatoes soften slightly.
Pour in 1/2 cup chicken broth and bring to a simmer. Let it reduce slightly for 2 minutes. Then, stir in 1/2 cup heavy cream and continue cooking until the sauce thickens, about 3-4 minutes. Season with salt and pepper to taste.
Return the cooked chicken to the skillet, along with the drained pasta. Toss everything together gently to coat the pasta evenly in the creamy sauce. If the sauce feels too thick, add a splash of the reserved pasta water to loosen it up.
Remove the skillet from heat and sprinkle 1/4 cup grated Parmesan cheese over the pasta. Toss until the cheese melts into the sauce. Garnish with fresh basil leaves before serving.