Any dramas or movies where the female lead is average looking and doesn't get noticed but the male lead falls for her because of her personality or loving/simple nature? 

I know actresses are generally good looking so this might be a hard one but I hope someone can help out.

A few dramas that somewhat follow this trend are:

Meteor Garden 

Personal Taste

Tomorrow With You

Kyou wa Kaisha Yasumimasu

Preferably the show isn't set in high school. University or work or co-habitation or even arranged marriage set-up will work. Basically any plot that involves adults.

 ColourMePurple:
Any dramas or movies where the female lead is average looking and doesn't get noticed but the male lead falls for her because of her personality or loving/simple nature? 

 ColourMePurple:
Preferably the show isn't set in high school. University or work or co-habitation or even arranged marriage set-up will work.

A beautiful actress plays a girl who was pretty but is now "ugly", an "ugly" girl that disguises herself as pretty, or a pretty girl who disguises herself as "ugly":

The narrative frames the FL as "plain" or very tomboyish, or the ML thinks the FL is a boy when he starts to fall for her:

She Was Pretty,  Cheese in the Trap and Attention Love seem to fit best. Thanks for these.

The girls in True Beauty, Accidentally in Love and Ugly Duckling aren't ugly. If anything, they look better than average. The girls don't have to be "ugly". They just have to be ordinary and their plus point for the male lead should be their personality or even attitude. 

As for cross-dressing, I presume that has more to do with sexuality rather than looks. Especially if the male lead doesn't know that the person he is falling for is a female. 

The highlight of their relationship should be that he likes her for her personality not because she is trying to be more pretty or that she changed her looks to become more attractive. If anything, he should like her the way she is. Sort of like in Extraordinary Attorney Woo, he likes her quirks or despite that. But the show doesn't explore the relationship much. Also, she is quite brilliant which is far from being a plain Jane.

I just watched Busu no Hitomi Ni Koishiteru- she's not ugly, she's just plus sized, but the ML falls for her personality and calls her his angel. There is an older 2006 version, and i think she's a little more average looking than the version that I saw.

Down with Love - also sort of fits, it's been a while since I watched it but he hires a tomboy who he thinks is a lesbian to be the nanny to his niece and nephew, slowly by spending time getting to know her he falls for her.

My Lovely Sam Soon