Heat 2 tbsp sunflower oil in a large pan, add 1 finely chopped onion, 2 sliced garlic cloves and 1 tbsp chopped ginger, and fry for about 3 mins.
Stir in 500g potatoes, cut into 2cm chunks, 1 halved, deseeded and finely sliced red chilli, ½ tsp black mustard seeds, ½ tsp cumin seeds, ½ tsp turmeric, and ½ tsp salt and continue cooking and stirring for 5 mins more.
Add a splash of water, cover, and cook for 8-10 mins.
Check the potatoes are ready by spearing with the point of a knife, and if they are, add 250g spinach leaves and let it wilt into the pan. Take off the heat and serve.