In a large Dutch oven or covered casserole, layer the ingredients in the following order: lamb cubes, sliced potato, sliced onions, sliced celery, sliced carrots, sprinkling each layer with salt, pepper, and thyme.
Add the water to the pot, cover, and slowly bring to a boil over medium-low heat.
Let simmer for 5 minutes, then transfer the pot to the oven and bake, without lifting the lid or stirring, for 2 to 2 1/2 hours or until the lamb is tender.
Sprinkle with chopped parsley, stir very gently to mix (the potatoes will be very soft) and serve.
Recipe from http://www.fullersedinburg.com/recipes/irish_stew.htm.