I got this recipe from Allrecipes.com which has pretty much gotten me through being away from my cook books. I have made some changes to it (I think for the better) but if you are interested in the original recipe, you can check it out here.
2 zucchinis (or however many you need for the right volume)
touch of oil
green pepper, sliced
clove of garlic, chopped
jar spaghetti sauce
fresh mozzarella, sliced
Heat the oil in a pan and saute the green peppers, onions and garlic. Add the zucchinis and cook until soft. Pour in the sauce and heat until heated through.
Meanwhile, cut open the bread and lay the cheese slices on one side (or two if you like a lot of cheese). Put on a cookie sheet and cook until the cheese melts. (I didn't really notice the temperature and you can use the broiler but watch it carefully.)
Once the cheese is melted, top with the zucchini mixture and serve. The cheese helps hold it together but it is still pretty messy. It would also be good with mushrooms in the mix. We like to have it with potato salad or the like.