Toss sliced onions with salt and lemon juice. Squeeze the onions a bit as you toss. Let them steep until you need them. This can be made up to 2 weeks in advance and refrigerated.
Flatbreads:
Add the flour, yogurt, baking powder, olive oil, and salt to a large bowl. Add enough water to make a shaggy dough. Tip out onto your counter and knead to a smooth ball. Set aside for 15 mins.
Divide into 6 pieces. Roll them out using more flour if necessary to avoid sticking. Lightly oil a pan and cook on both sides. Place them one on top of the other in a hot pack or in a loosely bundled cloth. Set aside.
Tzatziki:
Grate the cucumbers and squeeze out all the excess moisture from them. Add to a bowl and mix in yogurt, garlic, and salt. Set aside.
Jackfruit:
Add the jackfruit, smoked paprika, chilli powder, oregano, cumin, pepper and salt to a bowl. Toss the jackfruit in this spice mix. Break up some of the bigger pieces with your fingers.
Heat 2 tablespoons of olive oil in a pan and cook the jackfruit until nicely browned. Add more oil if necessary.
To serve: Spread a dollop of tzatziki on your flatbread. Top with a generous amount of jackfruit meat, and sliced tomatoes and pickled onions.