"Do you want toast?"
Translation:Dych chi eisiau tost?
Anyone know why Duolingo gave me 'moyn' instead of 'eisiau' here.
Probably because you wrote Dych chi'n eisiau tost? or something similar, with 'n in it.
eisiau does not take yn before it. It's just Dych chi eisiau tost?
However, the synonym moyn is a regular verb and does require yn when used with a form of bod, e.g. Dych chi'n moyn tost?