Cut the potatoes into same-sized chunks then boil until soft, then drain. Mash with butter, season with pepper then stir through the herbs. Reserve 500g of potato for lunch.Finely dice onions then fry on a pan with a little rapeseed oil until they turn translucent. Crush in the garlic and fry for a further minute then add the tinned tomatoes and tomato puree.Let the sauce simmer for about 12-15 minutes until it has turned lovely and thick then mix in the spices, vinegar, lime, and beans and stir well. Reserve 400g of beans for lunch.Pour the remaining beans into an ovenproof dish, then cover with the mashed potato. Use a spoon to flatten down, then a fork to fluff up the potato which will help it go lovely and crispy.Bake at 180ºC for 30 minutes. Serve warm.

To make Potato Farls with leftovers:Mix the potato and flour together until fully combined. Shape into palm-sized cakes, then fry on a dry pan until golden brown on both sides.Serve in a lunchbox with a portion of cold beans and fruit.