Place the mash in a large bowl, then slice the spring onions.
Set a medium saucepan on a medium heat. Add a little splash of oil, followed by the spring onion. Cook for about 10 minutes or until just starting to soften.
Spread the breadcrumbs out on a baking tray. Bake in the oven for 5 to 7 minutes to dry out, then set aside. Raise the oven temperature to 200ºC/gas 6.
Tip the spring onion into a food processor with the corn, peas and leftover veg. Pick the parsley leaves and put to one side, then place the stalks in the processor.
Pulse to just combine, then use a rubber spatula to scrape the mixture into the bowl with the potato.
Mix together, then season with a tiny pinch of sea salt and black pepper and a scraping of lemon zest. Alternatively, mash everything together with a potato masher in the large bowl.
Line a baking sheet with greaseproof paper. Split the veg mixture into 12. Roll each into a ball and shape into fingers.
Place each finger on the tray, then chill in the fridge for 10 minutes or so to firm up.
Now it’s time to set up a little production line: tip the flour into a shallow bowl and mix in the paprika. Crack the eggs into another bowl and whisk well with a fork. Tip the breadcrumbs into the final bowl.
Take the fingers from the fridge. One at a time, coat them in flour, dip in the egg, letting any excess drip off, and then roll in breadcrumbs.
Place back on the tray, drizzle with oil and bake for 12 to 15 minutes, or until golden and cooked through.
In the meantime, prepare your sandwiches. Discard the outer leaves from the lettuce, then break off the nice, smaller ones. Rinse, pat dry with kitchen paper and set aside.
In a small bowl, mix the mayonnaise and yoghurt together with a little squeeze of lemon juice. Cut the rolls in half.
When the fingers are ready, remove from the oven. Fill the buns with the fingers, lettuce, parsley leaves, mayonnaise mixture and top with a snipping of salad cress. Delicious served with sweet potato wedges.