Preheat oven to 350°.
Bring a large pot of water to a boil over high heat and add about a 1/2 teaspoon of Cajun seasoning. Add the mirliton, lower the heat and cook for 30 to 45 minutes until it is the consistency of a soft potato. Drain mirliton. Put a knife in the crease, cut the mirliton in half lengthwise. Scoop out the pulp, leaving at least 1/4-inch all around. Set pulp aside. Turn upside down to let them mirliton drain.
In skillet over medium heat melt butter and add chopped vegetables until soft; about 5 to 10 minutes. Chop the mirliton pulp and add to skillet. Add remaining 1/2 teaspoon of Cajun seasoning and the shrimp and stir to combine. Stir in the breadcrumbs and season with salt and pepper, to taste.
Place mirliton halves into a casserole dish. Scoop shrimp mixture into mirliton shells and bake for 30 minutes.