Place half of the spinach in water and salt in large saucepan; cover. Cook on medium heat 5 to 8 min. or until spinach is wilted, stirring often.
Remove spinach with tongs; drain in colander. Repeat with remaining spinach. Cool slightly.
Mix spinach and onion; divide mixture into 6 portions. Squeeze out excess water. Using your hands, form little "nests", making small indentation in center.
Place nests in baking dish; place 1 cream cheese piece into center of each nest.