Bring a large pot of salted water to a boil. Cook the tortellini according to package directions until al dente. Drain and set aside.

If marinating, place chicken pieces in a bowl with buttermilk, cover, and refrigerate for 4 to 6 hours. Drain before using. If not marinating, pat chicken dry with paper towels.

In a small bowl, combine paprika, Italian seasoning, salt, and pepper. Toss the chicken pieces with the seasoning mixture, then sprinkle with flour and stir until evenly coated.

In the same pot used for the tortellini (make sure it's nonstick), heat 3 tablespoons of the oil from the sun-dried tomato jar over medium heat. Add the basil sprig and garlic, stirring for about 30 seconds until fragrant.

Increase heat to medium-high and add the seasoned chicken. Cook, stirring occasionally, until the chicken is golden and cooked through, about 6 to 8 minutes. If needed, add a little more sun-dried tomato oil to prevent sticking.

When the chicken is nearly done, remove the basil sprig. Stir in the chopped sun-dried tomatoes and cook for another minute until heated through.

Return the drained tortellini to the pot with the chicken. Reduce heat to low and gently stir for 1 to 2 minutes to warm through.

Remove from heat. Stir in the basil pesto and 1 to 2 tablespoons of additional sun-dried tomato oil if desired. Taste and adjust seasoning with salt, pepper, or red pepper flakes.

Divide among plates and garnish with fresh basil and grated Parmesan cheese. Serve immediately.