01 - Bring a large pot of salted water to a rolling boil. Add the fettuccine and cook according to package directions until al dente. Reserve 1/2 cup of starchy pasta water before draining. Set the drained pasta aside.
02 - Pat the chicken pieces and shrimp dry with paper towels. Season both lightly and evenly with salt and freshly ground black pepper.
03 - Heat 1 tbsp olive oil in a large skillet over medium-high heat. Add the seasoned chicken pieces in a single layer and sauté for 5-6 minutes, turning occasionally, until golden brown and cooked through to an internal temperature of 165°F. Transfer to a plate and tent loosely with foil.
04 - Add the remaining 1 tbsp olive oil to the same skillet. Sear the shrimp for 2-3 minutes, flipping once, until they turn pink and become opaque throughout. Remove and set aside with the chicken.
05 - Reduce the heat to medium. Melt the butter in the skillet, then add the minced garlic. Sauté gently for about 1 minute, stirring constantly, until fragrant and lightly golden — do not allow the garlic to brown.
06 - Pour in the heavy cream and bring to a gentle simmer. Stir in the grated Parmesan, lemon zest, lemon juice, red pepper flakes (if using), salt, and pepper. Continue simmering for 2-3 minutes, stirring frequently, until the sauce coats the back of a spoon.
07 - Return the chicken and shrimp to the skillet. Add the cooked pasta and toss everything together thoroughly, incorporating reserved pasta water a splash at a time until the sauce reaches your preferred consistency.
08 - Fold in the chopped fresh parsley. Taste the dish and adjust salt and pepper as needed.
09 - Divide among warmed plates or bowls. Finish each portion with a generous shower of freshly grated Parmesan and a lemon wedge on the side.