Bring a large pot of salted water to a boil. Add the rigatoni and cook according to package instructions until al dente, usually about 10-12 minutes. Drain and set aside, reserving about 1/2 cup of pasta water for later.
While the pasta cooks, heat olive oil in a large skillet over medium heat. Add the chopped onion and diced bell pepper, sautéing until softened, about 4-5 minutes. Stir in the minced garlic and cook until fragrant, about 1 minute. Add the ground turkey and cook, breaking it up with a spoon, until fully browned and cooked through.
Sprinkle the Cajun seasoning, smoked paprika, and cayenne pepper (if using) over the turkey mixture. Stir well to evenly coat the meat and veggies with the spices. Cook for another 2 minutes to let the flavors meld.
Pour in the chicken broth and heavy cream, stirring to combine. Bring the mixture to a gentle simmer and let it thicken slightly, about 3-4 minutes. Season with salt and pepper to taste.
Reduce the heat to low and stir in the shredded cheddar cheese until melted and smooth. If the sauce feels too thick, add a splash of the reserved pasta water to loosen it up.
Add the cooked rigatoni to the skillet and toss everything together until the pasta is thoroughly coated in the creamy Cajun sauce. Garnish with fresh parsley before serving.