01 - Bring a large pot of salted water to a rolling boil. Add pasta and cook according to package directions until al dente. Reserve 1/2 cup of starchy pasta water before draining. Set drained pasta aside.
02 - In a large skillet set over medium heat, melt the butter until it begins to foam. Add the minced garlic and sauté for about 1 minute, stirring constantly, until fragrant and lightly golden.
03 - Stir in the Dijon mustard, smoked paprika, crushed red pepper flakes, Worcestershire sauce, lemon zest, and lemon juice. Cook for 1 to 2 minutes, stirring frequently to blend the spices and prevent the butter from browning.
04 - Fold in the chopped parsley, chives, kosher salt, and black pepper. Stir well to evenly distribute the herbs throughout the sauce.
05 - Transfer the cooked pasta into the skillet with the sauce. Toss vigorously, adding the reserved pasta water a splash at a time, until a glossy, emulsified coating clings to every noodle.
06 - If using shredded chicken or grilled steak, fold it into the pasta now. Cook for an additional 2 minutes, tossing occasionally, until the protein is heated through.
07 - Divide among serving bowls immediately. Finish with extra fresh herbs, a generous shower of grated Parmesan cheese, and a squeeze of lemon from the garnish wedges.