01 - Bring a large pot of salted water to a rolling boil. Add fettuccine and cook according to package directions until al dente. Reserve 1/2 cup of starchy pasta water before draining. Set pasta aside.
02 - Pat chicken and shrimp dry with paper towels. Season both lightly with salt and freshly ground black pepper on all sides.
03 - Heat 1 tbsp olive oil in a large skillet over medium-high heat. Add chicken pieces in a single layer and sauté until golden brown and cooked through, about 5-6 minutes. Transfer to a plate and tent loosely with foil.
04 - Add remaining 1 tbsp olive oil to the same skillet. Sear shrimp for 2-3 minutes, flipping once, until pink, curled, and opaque throughout. Remove and set aside with the chicken.
05 - Reduce heat to medium. Melt butter in the skillet and add minced garlic, stirring constantly for about 1 minute until fragrant and lightly golden.
06 - Pour in heavy cream and bring to a gentle simmer. Stir in Parmesan cheese, lemon zest, lemon juice, red pepper flakes (if using), salt, and pepper. Let simmer for 2-3 minutes, stirring frequently, until the sauce coats the back of a spoon.
07 - Return chicken and shrimp to the skillet. Add drained pasta and toss everything together, gradually adding reserved pasta water as needed to reach your preferred sauce consistency.
08 - Fold in chopped parsley and taste the dish. Adjust salt, pepper, or lemon juice as needed to balance the flavors.
09 - Divide among warmed plates or bowls. Garnish generously with freshly grated Parmesan and serve with lemon wedges on the side. Serve immediately.