"The food was mostly in the form of very thin cakes, made of a meal that was baked a light brown on the outside, and inside was the colour of cream. Gimli took up one of the cakes and looked at it with a doubtful eye.
'Cram,' he said under his breath, as he broke off a crisp corner and nibbled at it. His expression quickly changed, and he ate all the rest of the cake with relish."
So it actually is more cake-like and crisp, rather than bread-like and chewy. You are correct.
Maybe something like arrowroot biscuits, only baked in thin squares?
Shortbread?