Fill a large pot with water, add salt, and bring to a boil. Add pasta and cook until al dente, about 8-10 minutes. Reserve 1/2 cup of pasta water, then drain.

In a skillet, melt 2 tablespoons of butter over medium heat. Season chicken with salt, pepper, and paprika. Cook chicken for 6-8 minutes on each side until golden brown and internal temperature reaches 165°F.

Remove chicken from skillet. Add remaining butter and minced garlic. Sauté until fragrant, about 1 minute.

Stir in Dijon mustard, lemon juice, lemon zest, red pepper flakes, and thyme. Cook for another minute.

If using heavy cream, add it now and let the sauce simmer for 2-3 minutes until thickened.

Return chicken to skillet, add drained pasta, and toss together, adding reserved pasta water as needed for creaminess.

Stir in Parmesan cheese and parsley. Taste and adjust seasoning with salt or pepper. Serve warm, garnished with more Parmesan and parsley.