Preheat oven to 350 degrees F (175 degrees C). Line a baking sheet with aluminum foil.
Scoop seeds and flesh from zucchini halves with spoon, leaving hollowed-out shells. Discard about half the flesh. Put remaining flesh in a large bowl.
Mix ground beef, tomato soup, water, bell pepper, bread crumbs, egg, Italian seasoning, and garlic powder with the zucchini flesh; spoon into the zucchini shells. Arrange stuffed zucchini onto the prepared baking sheet.
Bake in preheated oven for 25 minutes.
Sprinkle Italian cheese blend over the zucchinis and continue baking until the cheese is melted and bubbly, about 10 minutes more.
