Oil the bottom of a baking dish large enough to hold all the potatoes and mushrooms. Lay down a layer of potato, then a layer of the mushrooms (including some of the reconstituted dried mushrooms if using), season with salt and pepper, and finally top with the breadcrumb mixture. Drizzle some olive oil on top. Repeat these steps until you've used up all the ingredients. But before laying on the final breadcrumb topping, drizzle a bit of water, broth or, if you're using the reconstituted dried mushrooms, some of their soaking liquid, filtered of any grit, down the inside edge of the baking dish, taking care not to upset the ingredients.