Peel mirliton and cut in chunks. Boil in salted water about 15 minutes or until tender. Drain and then mash mirliton. Set aside.
Cook down ground beef, onions, celery, bell pepper, green onions, and garlic until browned. Drain grease.
Add mirliton to beef mixture and mix. Add salt and pepper to taste. Continue to cook out liquid. Remove from heat and add 1/4 cup breadcrumbs.
Butter a casserole dish and spoon in mixture. Top with breadcrumbs and pats of butter. Bake at 350 degrees for 30 minutes or until breadcrumbs are browned.
(This goes great with field peas.)