NP-hard problems on expander graphs?
If "unbalanced expanders" count as expanders for the purpose of this question (an unbalanced expander: a bipartite graph $G=(A,B,E)$, such that for every subsets $A'\subseteq A$, $B'\subseteq B$, the fraction of edges between $A'$ and $B'$ is about ${|A'||B'|}/{|A||B|}$), then yes, many problems on expanders (e.g., constraint satisfaction problems) are NP-hard to approximate.

In particular, the proof of the two-query, low error, PCP Theorem [with Ran Raz in 2008] constructs expander graphs.