01 -  Bring a large pot of salted water to a boil and cook penne pasta until al dente; drain and set aside. 
 02 -  Sauté peeled shrimp with Cajun seasoning in a skillet over medium heat until pink and opaque, about 3 minutes. 
 03 -  In a large bowl, mix cooked penne, sautéed shrimp, Alfredo sauce, and diced bell pepper until thoroughly combined. 
 04 -  Transfer the mixture into a baking dish and evenly sprinkle shredded mozzarella cheese over the top. 
 05 -  Bake in a preheated oven at 375°F for 20 minutes, or until cheese is golden and bubbling.