Na-adjective (keiyodoshi), Noun which may take the genitive case particle 'no', Noun
easy; smooth; without a hitch; quick
most frequently used adverbially as 〜にsee トントン
この国の経済は近年とんとん拍子に成長しています。This nation's economy is growing by leaps and bounds in recent years.
Also written とんとん拍子【とんとんびょうし】