Bring a large pot of salted water to a boil. Cook pasta according to package directions. Reserve 1 cup of pasta cooking water, (plus more is needed) then drain pasta. Keep empty pot hand for later.
Mince garlic. Zest and half lemon.
While pasta cooks, pat chicken dry with paper towels, and season all over with Italian seasoning, salt and pepper. Heat a drizzle of oil in a large pan over medium-heat, cook chicken 3-5 minutes a side, until cooked through.Turn off heat: transfer to a cutting board to rest.Once cool enought to handle, chop chicken.
Heat a drizzle of oil in the pan used for spaghetti, over medium high heat. Add garlic, lemon zest and pinch of chili flakes (optional). Cook, stirring until fragrant, 20-30 seconds.Stir in pasta water, bouillon cube, and juice from both lemon halves. Simmer for 2-3 minutes until thickened. Turn off heat.
Add drained spaghetti, sour cream, and butter to pot with sauce; toss to coat.
Add the Parmesan cheese and season with salt and pepper. Tip; If needed, stir in more reserved pasta water a splash at a time, untiil spaghettie is coated in a creamy sauce.
Divide between bowls. Top with chicken and additional Parmesan cheese, and a pinch of chili flakes if desired.Enjoy!