Bathroom floor prep for laying tile.

I'm doing a bathroom remodel and tackling the flooring. I've removed the old tile but as you can see in the picture there is thinset on this particle board I need to get up as well as thinset on the actual subfloor underneath. Been kinda a pain i the ass. Any tips on how I should best approach this. Scrap off thinset from subfloor or just layer over like the last person did?