I think you should have access to flagship first dining at the D30 Flagship lounge in Miami (I had it on a recent BA flight number which was operated by AA) but you can ask when you get there if they don't offer you a voucher/ticket/pass when you check in with the lounge agent. Anyway, even if you don't the lounge is still good and there should be a small Cuban/Mexican station in the back right corner serving something interesting besides the buffet.