1. Slice each chicken breast in half horizontally to create thin cutlets. Season both sides with salt and pepper.

2. Heat a large skillet over medium heat and add the butter. When melted, add the chicken in a single layer and cook for 3-4 minutes per side until golden brown and just cooked through. Transfer to a plate and cover to keep warm.

3. In the same skillet, add the chopped onion and cook until softened, about 5 minutes. Add the minced garlic and cook 1 minute more until fragrant.

4. Add the sliced mushrooms to the skillet and cook until they release their liquid and start to brown, 6-8 minutes.

5. Stir in the drained kidney beans, sun-dried tomatoes, heavy cream, Dijon mustard, and half the parsley. Simmer the sauce for 5 minutes, stirring occasionally, until slightly thickened.

6. Return the cooked chicken and any accumulated juices to the skillet. Nestle the chicken into the sauce and simmer together for 2-3 minutes to heat through. Stir in the baby spinach and cook just until wilted, about 1 minute.

7. Meanwhile, bring a large pot of salted water to a boil. Cook the fettuccine according to package directions until al dente. Drain well.

8. Add the hot, drained pasta directly to the skillet and toss gently until the pasta is evenly coated in the sauce and ingredients are well distributed.

9. Serve the creamy chicken and mushroom pasta hot, garnished with the remaining parsley and freshly grated Parmesan cheese. Handle hot plates and skillet carefully to avoid burns.