Cut squash and cucumber into crosswise slices one-quarter-inch thick. Place squash in a saucepan with one-halfinch of boiling water containing the salt. Cover and bring to a boil. Reduce heat and cook for twelve minutes longer, or until almost tender.
Add the cucumber and cook only until crisp-tender, about three minutes. Drain, if necessary.
Sauté the green onions in the butter. Add to saucepan along with sour cream and black pepper. Mix lightly. Heat, but do not boil. Serve sprinkled with parsley.