Based on the research I've done (and you can google around to see the same thing) most HSA's charge an "account maintenance fee" of around $3.00 per month if you open an investment account. Some will waive or reduce the fee if you keep a minimum balance of your HSA ($2,000 to $5,000 or more) in their low-interest savings accounts.
So, if you have a $10,000 investment with the HSA, a $36 annual maintenance fee is equivalent to a 0.36% surcharge on top of any fund expense ratio. For the OP, if she goes with the Vanguard 500-index fund VFINX at 0.17% ER then add 0.36% for a total expense of 0.53%. This is about what an average 401(k) will charge. The higher your balance, of course, the lower the fee percentage since the fee is flat.
While I'm not happy about paying these fees, that's the market right now. We can hope that as HSA plans get more popular that the market will get more competitive and fees will go down. Your alternative to paying these fees is to let the money earn a meager ~0.25% in the HSA's savings account. I'd rather pay the fees and invest.
Also, it looks like Optum charges a $20 fee to transfer assets out of it into another HSA. This is not uncommon. Typically most HSA plans will not charge you to transfer money in, since they want your money and they don't want to discourage incoming transfers. This is why I recommended transferring only annually, if you decide to go that route.