Boil the pasta: Bring a large pot of salted water to a boil. Cook pasta until just shy of al dente, 1–2 minutes less than package directions. Reserve at least 1 cup of pasta water, then drain.

Season the chicken: Pat the chicken dry. Season generously with salt and black pepper. You can add a pinch of garlic powder or paprika for extra flavor.

Sear the chicken: Heat 1 tbsp olive oil in a large skillet over medium-high heat. Add chicken in a single layer. Cook 4–6 minutes, turning once, until golden and cooked through. Transfer to a plate.

Build the sauce base: Reduce heat to medium. Add remaining 1 tbsp olive oil and the butter to the same skillet. When the butter foams, add minced garlic and red pepper flakes. Stir 30–45 seconds until fragrant—don’t let it brown.

Add lemon: Stir in lemon zest and 3 tbsp lemon juice. Scrape up any browned bits from the pan. Add 1/2 cup reserved pasta water and bring to a gentle simmer.

Emulsify: Whisk or stir to bring the sauce together. It should look glossy, not oily. If it seems thin, simmer 1–2 minutes more. If it tightens too much, splash in more pasta water.

Toss everything: Add the drained pasta and cooked chicken to the skillet. Reduce heat to low. Sprinkle in the Parmesan and toss continuously until the cheese melts and the sauce coats the pasta. If using spinach, peas, or tomatoes, fold them in now. Adjust with extra pasta water as needed for a silky texture.

Taste and finish: Taste and adjust with salt, more lemon juice, or black pepper. The flavor should be bright but balanced. Garnish with chopped parsley and extra Parmesan.

Serve: Plate immediately while hot and glossy. Add a light drizzle of olive oil if you like.