Pierce mirlitons with a fork. Place in a Dutch oven; cover with water. Bring to a boil over high heat; reduce heat, and simmer 30 minutes or until tender. Drain and cool. Cut mirlitons in half lengthwise; discard seeds. Scoop out pulp, leaving a 1/4-inch-thick shell. Chop pulp; place in a large bowl.
Preheat oven to 375°.
Melt butter in a medium nonstick skillet over medium heat. Add onion and garlic; cook 6 minutes or until onion is tender. Add onion mixture, crawfish, and remaining ingredients to chopped pulp; stir to combine.
Spoon about 1/2 cup crawfish mixture into each shell; place stuffed mirlitons on a baking sheet. Bake at 375° for 30 minutes or until crawfish mixture is thoroughly heated and golden.