unarmed strike, using the burning blade boost for more damage. since I doubt he can miss it, he'll also fight defensively.
If an unarmed strike would be ineffective (which I think he'd probably know better than I), he'll draw his sword and use that instead, but won't use the burning blade, since that would leave him with no actions left to move away with.
Assuming he succeeds, he'll use his move and/or travel devotion action to drag the shield through the resulting hole.
unarmed attack
Rolled 1d20+4 : 9 + 4, total 13
damage
Rolled 1d4+3 : 3 + 3, total 6
fire
Rolled 1d6+3 : 1 + 3, total 4