For the marinade, whizz all the ingredients together in a food processor until no big chunks remain (it doesn’t have to be perfectly smooth). If there are any really big chunks of jackfruit, cut them a bit smaller – they shouldn’t be bite-size, but probably not much bigger than two-bite size. Coat the jackfruit in the marinade and leave in the refrigerator for at least two hours, and up to three days. For the seasoned flour (if using), stir together all the ingredients until the seasonings are well distributed.
To cook, pour the oil into a very deep, wide saucepan, to come no higher than halfway up the sides and heat to 180°C (350°F).
Remove the jackfruit from the marinade, letting any excess drip off, and dredge in the cornflour or seasoned flour, ensuring that all the nooks and crannies are well coated – this will help maximise crunch and help keep the sugars in the marinade from burning.
Carefully lower the jackfruit into the oil in small batches, checking the temperature periodically to ensure it is still around 180°C (350°F), and fry for about five minutes, until the crust is golden brown. Remove the jackfruit with a slotted spoon and drain on paper towels; if you’re not using the seasoned flour, finish with a few pinches of salt and pepper. Serve with Vegan Japanese Mayo, Ponzu, or just good old soy sauce and perhaps a wedge of lemon.