Directions

1. Bring water to a boil in a large Dutch oven over high heat. Cook pasta according to package directions. Reserve 1/2 cup cooking water; drain well. Wipe the pot clean.
2. Heat oil in the pot over medium-high heat. Add onion and 1/4 teaspoon salt; cook, stirring often, until softened, 4 to 5 minutes. Add spinach and garlic; cook, stirring occasionally, until the spinach is bright green and wilted, 3 to 4 minutes. Reduce heat to medium-low. Add half-and-half, Gruyère, cream cheese, mustard, lemon zest, lemon juice, crushed red pepper, black pepper and the remaining 1/2 teaspoon salt; cook, stirring constantly, until the cheese is melted and the mixture is mostly smooth, about 2 minutes.
3. Stir in the pasta, chicken and parsley, adding the reserved cooking water, 2 tablespoons at a time, if needed, to keep the sauce loose and creamy. Cook until the pasta and chicken are coated and warmed through, about 1 minute. Divide among 8 bowls; garnish with additional parsley and black pepper, if desired.