Cook the whole-wheat penne according to package directions. In a large pot, heat olive oil and cook onion until softened. Add spinach, garlic, and seasonings. Reduce heat and add half-and-half, Gruyère cheese, cream cheese, mustard, lemon zest, and lemon juice. Stir in the cooked pasta, shredded rotisserie chicken, and parsley. If needed, add reserved cooking water to keep the sauce creamy. Serve in bowls and garnish with additional parsley and black pepper. This dish is high in protein and packed with flavor.