Boil mirlitons for 45–60 minutes until tender. Drain, cool, cut in half, remove seeds, scoop pulp, mash, and press out excess water.
In the same pot, cook the seasoning blend with butter for 5 minutes.
Add mirliton pulp, stuffing mix, Cajun seasoning, salt, and pepper. Cook on low for 8–10 minutes, stirring occasionally.
Stir in garlic and shrimp. Cook until shrimp turn pink. Adjust seasoning if needed.
Preheat oven to 350°F and grease a 9x11 pan. Spread mixture in the pan, sprinkle with breadcrumbs and Parmesan, and bake uncovered for 25–30 minutes until golden.