Bring a large pot of salted water to a boil. Cook the cheese tortellini according to the package directions until just tender. Reserve about 1/2 cup of pasta water, then drain and set aside.
While the tortellini cooks, season the chicken pieces with Italian seasoning, garlic powder, salt, and black pepper.
Heat the olive oil in a large skillet over medium-high heat. Add the chicken and cook for 5–7 minutes, stirring occasionally, until golden brown and cooked through. Transfer the chicken to a plate and set aside.
Reduce the heat to medium. Add the minced garlic and sun-dried tomatoes to the same skillet. Cook for about 30–60 seconds, stirring constantly, until fragrant.
Pour in the chicken broth and scrape up any flavorful browned bits from the bottom of the skillet. Let it simmer for 2 minutes.
Reduce the heat to medium-low and stir in the heavy cream. Allow the sauce to gently simmer for 2–3 minutes without boiling rapidly.
Gradually stir in the freshly grated Parmesan cheese until melted and the sauce is smooth and creamy.
If using spinach or red pepper flakes, add them now and cook until the spinach is just wilted.
Return the cooked chicken to the skillet, then add the drained tortellini. Gently toss everything together until evenly coated in the creamy sun-dried tomato sauce.
If the sauce is too thick, add reserved pasta water one tablespoon at a time until it reaches your desired consistency. Taste and adjust the seasoning as needed.
Remove from the heat and let the dish rest for 2–3 minutes. Garnish with fresh basil, parsley, or additional Parmesan before serving.