Bring a large pot of salted water to a boil. Add fettuccine pasta and cook according to package instructions until al dente, about 8-10 minutes. Reserve 1 cup of pasta water before draining.

In a large skillet, heat a tablespoon of olive oil over medium-high heat. Season chicken breast with salt and pepper. Cook for 5-7 minutes on each side until golden brown and fully cooked with internal temperature of 165°F. Remove chicken and let it rest before slicing.

In the same skillet, add more olive oil if needed. Reduce heat to medium, add minced garlic and sauté for 1-2 minutes until fragrant. Pour in heavy cream, bring to a gentle simmer, and stir in Parmesan cheese until fully melted.

Add drained pasta and sliced chicken to the skillet. Toss gently, adding reserved pasta water gradually until the sauce reaches desired consistency.

Plate the pasta, garnishing with extra Parmesan and red pepper flakes if desired. Optionally toss in spinach before serving. Enjoy warm.