Cook the pasta in a large pot of salted boiling water according to package instructions until al dente, about 8-10 minutes. Reserve ½ cup pasta water, then drain and set aside.

In a large skillet, melt the butter with olive oil over medium heat. Add onion and red bell pepper, sauté for 3-4 minutes until softened. Stir in garlic, Cajun seasoning, and smoked paprika; sauté for another 1-2 minutes.

Pour in heavy cream and chicken broth, stir to combine, and bring to a simmer for 5-7 minutes. Add Parmesan cheese and lemon juice, stirring until cheese melts and sauce thickens. Season with salt and pepper to taste.

Gently fold in the lump crab meat and warm on low heat for 2-3 minutes until heated through, being careful not to break up the lumps.

Add the reserved pasta to the sauce, tossing gently to combine. If too thick, add reserved pasta water gradually until desired consistency is reached.

Serve the Cajun Crab Pasta in bowls, garnished with chopped parsley and extra Parmesan cheese if desired.