From Longman Dictionary of Contemporary Englishsoup/dish/fish etc of the daysoup/dish/fish etc of the dayDFa soup, meal etc that a restaurant serves on a particular day in addition to the meals they always offer → day
Examples from the Corpus
soup/dish/fish etc of the day• A little skimmer bream is my fourth fish of the day and the first I have had to net.• The fish of the day, a grilled sole, was of the same ilk. 