I would lobby my employer to change their HSA custodian to Fidelity if possible.
I would either roll over from your current HSA to Fidelity periodically, or, if you find that process too tedious, I would stop using the employer's HSA and just make contributions directly to a Fidelity HSA. Direct contributions mean you will not get the benefit of avoiding FICA taxation on those HSA contribution amounts, but that may be a price worth paying for simplicity and peace of mind. As the previous poster notes, the lack of investment options and time out of the market may actually be more costly than paying FICA on the contributions. You'll still get the income tax benefit of the HSA contributions by filling out Form 8889 with your tax return.