'mngan' actually is not indonesian language. But there is a word that spell almost like 'mngan', the word is 'mangan'. 'mangan' in indonesian language is a word for metal. Do you now Mg? Magnesium? In indonesian language it called 'mangan'.
in the other hand 'mangan' have a diferent meaning. if you know indonesian have an ethnic called Javanese, 'mangan' is one of javanese word that has mean 'eat'. for example if you want to ask "have you eat?" you can say "mangan durung?" in javanese casual way. PS: that sentence only can be use with friend you can't use it when you talk with people older than you.
I hope it can help you.