Shopping King Louie for sure, the first one to come to mind. Definitely fits the bill with an innocent, naive and clumsy male lead.
Empress Ki also fits the bill in a sense (and also stars Ji Chang Wook), but I'll make an emphasis to say that this is a much heavier, melodramatic historical drama and touches some very dark topics later on in the series with regards to the initially naive and innocent Emperor.
If you enjoyed Healer (and are open to Chinese dramas) I'd also recommend Cambrian Period which shares some similarities with Healer (as the innocent seeming male lead also lives a double-life) but is more political.