Bring a large pot of salted water to a boil. Add the bowtie pasta and cook according to package directions until al dente. In the last 3 minutes of cooking, add the broccoli florets. Reserve 1/2 cup of pasta water before draining. Drain and set aside.

Season the chicken pieces with Cajun seasoning, garlic powder, smoked paprika, salt, and black pepper. Toss until evenly coated.

Heat olive oil in a large skillet over medium-high heat. Add the seasoned chicken in a single layer and sear undisturbed for about 2 to 3 minutes. Turn and cook until golden brown and fully cooked through, about 6 to 7 minutes total.

Lower the heat to medium. In the same skillet, add the butter and allow it to melt, scraping up the browned bits from the bottom. Add the minced garlic and cook for 1 minute until fragrant.

Stir in the red pepper flakes (if using), Dijon mustard, lemon juice, and lemon zest. Add parsley and chives, then season with salt and pepper to taste.

Return the cooked chicken, pasta, and broccoli to the skillet. Toss everything to coat in the sauce. Gradually add reserved pasta water, a small splash at a time, until the sauce is smooth and silky.

Stir in the grated Parmesan cheese until melted and creamy. Serve warm, topped with extra Parmesan and fresh herbs if desired.