Basically, slice zucchini in half and scoop out the insides, leaving a 1/4″ shell, and chopping and reserving the insides. (Some recipes suggested parboiling them first. I put them in the frying pan with a bit of boiling water for about 5 minutes, but after I had done the cutting and scooping.) Place in a greased baking dish.
Saute chopped onions, celery, mushrooms and garlic in a bit of olive oil. After a few minutes add the reserved zucchini and some chopped tomatoes. Season with salt and pepper, and whatever else you desire. When soft, combine that mixture with bread crumbs (Wayne thought stuffing would be a great alternative), an egg and grated Cheddar cheese.
Spoon into the zucchini shells and top with a bit more grated cheese. Bake at 400 degrees for 15-20 minutes. Serve hot.