A variation that the family used to make (unfortunately I didn't get the recipe for the filling) was to use poppy seeds instead of ground walnuts.
there is a similar Polish cake with poppy seed filling. It is called makowiec (pronounced makovietz), though I'd translate that as "poppy seed cake" rather than "bread"... It is also a traditional Christmas cake in Poland.
Here are a few recipes that I found on the Web, although they are not gluten-free, I think you could try making them with a gluten-free flour substitute ( I never had enough patience to try to make gluten-free yeast dough myself, but the filling should be OK ).
here's a recipe for makowiec and for the poppy seed filling (and for a few more Polish cakes):
and a recipe for potica
I hope you enjoy it