From Longman Dictionary of Contemporary Englishslap-upˈslap-up adjective → slap-up meal/dinner etc
Examples from the Corpus
slap-up• Over £1,500 was raised at the fete and this will be used to give 200 pensioners a slap-up Christmas dinner.• I shall award a slap-up dinner at Jamash, our local Balti restaurant, to the winner.• To mark the occasion the club presented her with a tracksuit and treated her to a slap-up lunch at a Middlesbrough restaurant. 