Heat the oven to 190C/170C fan/gas 5. Oil and line a 500g loaf tin with two strips of baking parchment so it's fully lined, with an overhang at the top that could be folded over. Toss the potatoes with the oil and put in a small roasting tin.
To make the loaf, weigh out 125g jackfruit, choosing the pieces that have the most 'open' texture, then thinly slice. Tip into a bowl and stir in the tarragon, garlic and paprika.
Tip the rest of the jackfruit into a bowl with the eggs and dried mushrooms and blitz with a stick blender until very smooth. Add the chestnut purée, then blitz again until well mixed. Stir 150g of the mushroom mix with the sliced jackfruit. Spoon half of the remaining dried mushroom mix into the tin, then add the mushroom and sliced jackfruit mix, and cover with the rest of the dried mushroom mix. Press down and scatter over the cashews. Fold over the baking parchment and bake alongside the potatoes for 45 mins, or until firm.
Toss the lemon zest with the potatoes. Cover the loaf and leave it to rest while you cook the veg.
Tip 150ml water into a pan with the bouillon and leeks. Cover and cook over a medium heat for 2 mins. Add the asparagus and peas, then cover and cook for 2 mins more. Finally, add the spinach and stir to wilt. Add the lemon juice and the yogurt to the veg mix and stir well. If you're following our Healthy Diet Plan, serve half the veg with four slices of the loaf, reserving the remaining four slices and the rest of the veg for another night. Will keep for up to three days, covered, in the fridge. To serve on the second night, reheat the leftovers in the microwave until piping hot.