Peel and slice the cucumber. Scrub and slice the zucchinis, but do not peel. On the bottom of a 6-cup casserole, spread 3 slices of the crumbled bread. Arrange a layer of cucumber and zucchini over the bread. Dot this with 1 tablespoon butter or margarine; sprinkle with salt and pepper. Follow with another layer of vegetables, dot with 1 tablespoon butter and sprinkle with seasonings. Cover with crumbs from the remaining 2 slices of bread, and dot with the remaining tablespoon of butter or margarine. Pour the milk over all. Bake for 45 minutes in a 350 degree oven.