I track mined with a pair of accounts, one real and one virtual:
2019/01/01 Insurer
Income:Benefits -$100.00
Assets:HSA
(Funds:HSA) $100.00
2019/02/01 Doctor
Assets:Bank -$50.00
Expenses:Medical
(Funds:HSA) -$50.00
2019/02/15 Insurer Reimbursement
Assets:HSA -$50.00
Assets:Bank
The Funds:HSA shows the total amount still available for eligible expenses, and any difference between the two HSA accounts is an outstanding reimbursement.
Hope this helps.
Regards,
Ryan