Melt the butter in a large frypan over medium heat. Cook onion, capsicum, celery and garlic in butter until onions are tender. Stir in flour and cook for 5 to 10 minutes, stirring frequently. Stir in yabbies. Cover and simmer for 15 to 20 minutes, stirring often.
Stir in the cream, Cajun seasoning and cayenne pepper. Cover and simmer for about 20 minutes, stirring occasionally.
Meanwhile, bring a large pot of lightly salted water to a boil. Cook pasta in boiling water for 8 to 10 minutes or until al dente; drain.
Preheat oven to 180 degrees C. Butter a 20x30cm baking dish. Stir pasta into yabby mixture; pour into prepared dish and sprinkle with Parmesan cheese.
Bake in a preheated oven for 20 minutes, or until hot and bubbly.