Hello, slice master
It seems like you're facing a difficult situation with a curved wall and an uneven space. Both solutions you propose have potential, but let's discuss them further:
Level the gap with tile adhesive and glue the decorative wood panel directly
Align the gap with tile adhesive, let it dry, then glue the wooden panel with separate adhesive
I hope this helps and good luck with your project! If you have any additional questions or need further assistance, please ask.