Scrub the carrot and cut into small dice. Peel the garlic and the ginger and finely chop or grate both.
Pour 1 tbsp oil into a pan and bring to a medium heat. Slide in the carrot, garlic and ginger. Sprinkle in the ground cumin and a generous pinch of salt and pepper. Fry for 3-4 mins, stirring often, till the carrot is slightly softened.
Pour the lentils into the pan and crumble in the stock cube. Cover with 850ml boiling water and give everything a good stir. Return to the boil, then reduce to a simmer and cook gently for 20 mins, till the lentils are tender.
Meanwhile, trim any tough or dry stalks from the chard and discard. Roughly shred the leaves.
When the lentils are tender, stir in the chard for 1-2 mins, till wilted. Grate in the lemon zest. Have a taste and add a little extra salt and pepper if needed. Pour the soup into bowls and serve with wedges of lemon.