Cook the pasta: Boil in salted water until just shy of al dente.
Reserve 1 cup pasta water, drain, and set aside.
Prep the chicken: Pat dry, season with salt, pepper, Italian seasoning, and smoked paprika. Cut into bite-size pieces.
Sear the chicken: Heat olive oil in a large skillet over medium-high. Cook chicken 5–7 minutes until browned and cooked through.
Remove to a plate.
Sauté aromatics: In the same pan, add butter (optional), onion, and a pinch of salt. Cook 3–4 minutes. Stir in garlic for 30 seconds.
Build the sauce base: Whisk cornstarch into the chicken stock.
Pour into the pan, scraping up browned bits. Simmer 2–3 minutes until slightly thickened.
Make it creamy: Reduce heat to low. Stir in Greek yogurt and Parmesan until smooth.
If too thick, loosen with reserved pasta water. Season with salt, pepper, and a pinch of red pepper flakes.
Add greens and peas: Stir in spinach (and peas if using) until wilted and bright.
Combine: Add chicken and cooked pasta to the sauce. Toss gently over low heat to coat.
Finish with lemon zest and a squeeze of lemon juice for brightness.
Taste and adjust: Add more salt, pepper, or pasta water to get that silky, glossy texture.
Portion: Divide into 4–5 meal prep containers. Let cool uncovered for 10 minutes before sealing.