Cook the pasta: Bring a large pot of salted water to a boil. Cook the pasta until just al dente.
Reserve 1/2 cup pasta water, then drain.
Season the chicken: Pat the chicken dry. Season both sides with 1/2 teaspoon salt, 1/2 teaspoon black pepper, and the Italian seasoning.
Sear the chicken: Heat 1 tablespoon olive oil in a large skillet over medium-high. Add chicken and cook 4–6 minutes per side, until cooked through and browned.
Transfer to a plate to rest, then slice into strips.
Sauté aromatics: Reduce heat to medium. If the pan is dry, add another teaspoon of oil. Add garlic and cook 30–60 seconds until fragrant.
Stir in sun-dried tomatoes and a pinch of red pepper flakes.
Build the sauce base: Pour in the chicken broth and milk. Scrape up any browned bits. Simmer 2–3 minutes to warm through.
Make it creamy: Whisk the Greek yogurt in a small bowl to loosen.
Take the skillet off the heat for a moment, then whisk in the yogurt and Parmesan until smooth. Return to low heat; avoid boiling to prevent curdling.
Add greens: Stir in the spinach. Cook 1–2 minutes until wilted.
If the sauce gets too thick, add a splash of reserved pasta water.
Combine: Add the cooked pasta and sliced chicken to the skillet. Toss to coat. Taste and adjust with salt, pepper, lemon zest, and a small squeeze of lemon juice for brightness.
Finish and serve: Sprinkle with fresh basil and extra Parmesan.
Serve hot.