Boil the potatoes: Cook the potatoes for 8-10 minutes or until just tender. Drain.
Cook the spinach: While the potatoes are boiling, cook the spinach in a steamer over the potatoes for 3-4 minutes, or pierce the bag of spinach several times and cook in the microwave for 2-3 minutes or until wilted. Tip into a colander and drain, squeezing out most of the excess liquid by pressing with the back of a spoon.
Fry the onion and spices: Heat a large frying pan or wok with 3 tbsp oil. Add the onion and cook over a medium heat for 2 minutes, then stir in the ginger, chilli, ground coriander and turmeric. Cook for a few seconds, then add the potato cubes and stir-fry for 3-4 minutes. Separate the spinach leaves with two forks, then stir into the spicy potato mixture together with the lentils. Season to taste with salt. Heat gently until piping hot.
Complete the dish: While the potato mixture is warming through, heat the remaining oil in a small frying pan. Add the garlic shreds and cumin seeds, then cook for 1-2 minutes or until lightly browned. Stir in half the chopped coriander. Tip the potato and lentil mixture into a warmed serving dish and sprinkle with the garlic and cumin seed mixture and the remaining coriander.
Spicy root vegetables and french beans: Cut carrots into bite-sized chunks and cook in salted boiling water for 5 minutes or until barely tender. Drain. Cook the onion and spices, and add the root vegetables as step 3, omitting the lentils, then stir in 400g french beans and warm through. Add the spinach as before and serve with plain curd.