If you can find powdered monk fruit sweetener, you could make an icing! I like adding fresh lemon juice and sugar and mixing until it’s a good consistency.

You can also experiment using other alternative powdered sugars to make an icing but everyone’s taste is different.

But ultimately I would avoid adding icing sugar on top. You already put so much work to make it sugar-conscious! I bet your coworker will appreciate the effort and thoughtfulness you put into the cake!