can you put lemon rind/zest in a chocolate biscuit cake?

[MercuryInRetrograde]

Will it set?

My boss's daughter made a beautiful chocolate biscuit cake and it tasted fruity. Lemony and gingery.

Ps, the recipe was not disclosed despite my high praise

Yes you can. Zest isn't particularly wet and you wouldn't need much so there would be no need to adjust a standard recipe. She may have used lemon oil rather than zest though if there was no detectable texture from zest.