Add a bullet behaviour to both but disable by default.
Then on collision..
local anglePlayerEnemy
anglePlayerEnemy = angle( Player.X, Player.Y, Enemy.X, Enemy.Y )
Player 8direction disable
Player bullet set angle of motion to anglePlayerEnemy + 180
Player bullet enable
Enemy 8direction disable
Enemy bullet set angle of motion to anglePlayerEnemy
Enemy bullet enable
Wait 0.5
Player bullet disable
Player 8direction enable
Enemy bullet disable
Enemy 8direction enable
Set the bullet speed to something like 30.. you'll need to tweak this and the wait 0.5s to get the result you're after.