Yes, it is spelt Batwan not Batman!
Anyway I mistook this for a Vietnamese Star apple but realised it was not when the fruit felt really hard.
Apparently it is meant to be that hard because I thought it wasnt ripe.
Inside the fruit there are some seeds in the centre which are covered in white sticky slime.
The hard orange flesh is similar to the texture of unripe hami melon however the taste is extremely sour and used as a cooking ingredient.