Bring a large pot of salted water to a boil. Add the radiatori pasta and cook according to package instructions until al dente. Drain and set aside, reserving 1/2 cup of pasta water.
In a large skillet, heat olive oil over medium heat. Add the sun-dried tomatoes and sauté for about 2 minutes until fragrant.
Pour in the heavy cream and bring to a gentle simmer. Stir in the pesto sauce and mix until well combined.
Add the cooked pasta to the skillet, tossing to coat in the creamy pesto sauce. If the sauce is too thick, gradually add reserved pasta water until desired consistency is reached.
Stir in the arugula and grated Parmesan cheese. Cook for an additional 2-3 minutes until the arugula wilts. Season with salt, pepper, and red pepper flakes if using.
Serve immediately, garnished with extra Parmesan cheese if desired.