How to Make It
Preheat oven to 375°. Cut zucchini in half lengthwise; scoop pulp into a bowl, leaving 1/4-inch shells intact. Chop pulp. Microwave zucchini shells in a microwave-safe dish covered with plastic wrap at HIGH 4 minutes; transfer to a foil-lined jelly-roll pan.
Melt 2 Tbsp. butter in a skillet over medium heat; add chopped zucchini pulp, onion, next 4 ingredients, 1 1/2 tsp. salt, and 1/2 tsp. pepper, and cook 10 minutes. Stir in basil and 3/4 cup cheese.
Divide mixture among shells. Stir together breadcrumbs, melted 1 Tbsp. butter, and remaining cheese, salt, and pepper; sprinkle over stuffed shells.
Bake at 375° for 20 minutes or until thoroughly heated.