Zucchini are delicious here, but Sicilians use the pale green summer squash called cucuzze, which have a texture somewhere between cucumbers' and zucchini's. More Delicious, Quick Side Dishes
Heat the olive oil in a medium saucepan or deep skillet. Add the zucchini, potatoes, tomato, onion, celery leaves, basil and crushed red pepper and season with salt. Cover and cook over moderate heat until the vegetables are barely tender, about 25 minutes. Add the boiling water, cover and cook until the vegetables are tender, about 12 minutes longer. Season with salt and serve hot or at room temperature with Parmesan cheese.
The braised vegetables can be refrigerated overnight.