My basement kitchen wall is adjacent to the bathroom and shower. I want to replace the old tile in the kitchen with a straight wall, which I’m planning to paint. I have removed the old tile and found different material behind it. The top appears to be cement board and the bottom appears to be drywall screwed into the cement board. Behind this wall is a standing shower, which is also tiled. Can you please advise on what is the best way to replace this side of the wall with a straight wall that I can paint? Thank you.
Straight wall example: