I have a Wells Fargo HSA and I'm guessing I have the same options.
I keep the minimum cash required, that's $1000 in my case. The rest is invested in WFIOX, their S&P 500 fund with an expense ratio of 0.25%.
Interestingly, I can get an identical Vanguard fund in my 401(k) with an expense ratio of 0.04%.