Start a large pot of salted water. Add the pasta and cook until al dente. Reserve some pasta water before draining.

Season the chicken with salt and pepper. In a large skillet over medium-high heat, add olive oil. Sear the chicken until golden brown and cooked through. Remove the chicken from the pan and set aside.

Lower the heat and add butter to the skillet. Toss in the minced garlic and sauté for about 30 seconds until fragrant.

Pour in the heavy cream or chicken broth. Use a wooden spoon to scrape up the browned bits from the bottom of the pan. Let it simmer for a few minutes until it begins to thicken.

Stir in the parmesan cheese until the sauce is smooth. Return the chicken to the pan and add the cooked pasta. If the sauce is too thick, add a splash of the reserved pasta water.

Toss in the fresh spinach if using, and garnish with parsley and a squeeze of lemon juice for brightness.