I created this side dish when I was on South Beach Diet, and substituted the mushrooms for the breadcrumbs, or used whole wheat breadcrumbs. The bread crumbs are important because they soak up liquid from the shells cooking.
For a shortcut, or a lower fat dish, omit the oil, and microwave the chopped zucchini and garlic instead of sauteing. Microwave about 1 minute, drain, and continue.
If this is your only side dish, it serves four. If you're serving another vegetable or a salad, you could get by with one "boat" each, making the serving size 8.