To make the pickled fennel, place the sliced fennel in a bowl.

Bring the vinegar, salt, sugar and mustard seeds to a boil until the sugar has dissolved. 

Pour the hot pickling brine over the fennel and set aside. 

Drain and rinse the jackfruit pieces. 

Cutting from the longest point of each piece, slice the lengthways in to thin strips. 

Heat the oil in a medium saucepan or pot and sautée the Spanish onion and garlic for five minutes. 

Meanwhile, combine the cayenne pepper, paprika, oregano, onion powder, salt and sugar in a bowl.

Add the spice mix to the onion and garlic and stir for a minute.

Add the jackfruit slices and toss to coat in the spices.

Add the stock and bring up to a simmer. 

Cook for around 25 minutes, breaking the jackfruit up into "shreds" as you go, or until the stock is reduced down to a sauce. 

Remove from the heat and add the dijon mustard, stirring through. 

Taste and adjust seasoning if needed.

Slice open the burger buns and smear with a good dollop of vegan mayonnaise. Follow with a handful of rocket or baby spinach. Add a good spoon of pulled jackfruit followed by the pickled fennel to serve.