I had essentially the same question, but with wheat grass mats. Look down a couple of threads for one titled "potting mix".
Sadly, I don't have a personal answer... I haven't got my works yet!

I compost my microgreens and wheat grass mats after letting them dry out in the sun for a while.

Thanks, priswell! Do you throw them in the bins dry or get them damp again? or put them with other veggie scraps?

Why let them dry out first?