Currently you can as long as you didn't pay for it with any tax advantaged money like a FSA or HRA. At least that's my understanding, I don't have a HSA. How much proof you'd need that it was paid with regular money I dint know.
Also remember that if you are contributing to your HSA via paycheck, then you are avoiding all FICA taxes as well. So there is additional tax savings from using the HSA that you can never get by claiming the expenses on your taxes.
Well $2900 is already earmarked for HSA distributions. Removing that, I'm hovering around $7k in expenses. Which is barely enough to itemize for federal, and worth maybe $80 for state.
If I could afford to leave all the funds in the HSA and claim everything that would probably be the best option, but I would like to reimburse myself for expenses I put on a 0% credit card that is set to expire shortly.