In a saucepan over low-temperature, heat the Alfredo sauce. Bring a large pot of lightly salted water to a boil. Add pasta and cook for 8 minutes or until al dente; drain.
Boil prawns in a large pot of water until they turn orange, then place in bowl with melted butter. Let prawns marinate for 15 to 30 minutes; remove. In a large frypan over medium heat, saute the green capsicum and onion in a small amount of oil.
Mix together the cooked pasta, prawns, pepper-onion mixture and Alfredo sauce. Season with garlic powder and cumin.