Bring a large nonstick pot of salted water to a boil and cook the tortellini according to package directions; drain and set aside.
In a small bowl, mix paprika, Italian seasoning, salt, and pepper.
If marinating, drain chicken from buttermilk; otherwise cut chicken into even bite-sized pieces. Pat chicken dry with paper towels.
Toss the chicken with the seasoning blend, then add the flour and stir until pieces are lightly coated.
In the same large nonstick pot or a skillet, heat 3 tablespoons reserved sun‑dried tomato oil (or olive oil) over medium heat for about 30 seconds. Add the basil sprig and minced garlic and cook, stirring, for about 30 seconds.
Increase heat to medium and add the seasoned chicken. Cook, stirring occasionally, until the chicken is cooked through and no longer pink, adding more oil if needed.
When the chicken is almost done, remove the basil sprig, add the chopped sun‑dried tomatoes, and sauté until the chicken is fully cooked.
Return the drained tortellini to the pot with the chicken, reduce heat to low, and gently stir for 1–2 minutes to combine.
Stir in the basil pesto and 1–2 tablespoons of the reserved sun‑dried tomato oil as desired; taste and adjust seasoning with salt, pepper, and red pepper flakes if using.
Serve garnished with fresh basil and grated Parmesan if desired.