Heat the oil in a large saucepan or casserole dish. Peel and finely chop the onion and fry gently for 2-3 until starting to soften.Peel the ginger (a teaspoon is surprisingly handy for this job, give it a try!), then finely chop and add to the pan.
Peel and finely chop the carrots and add to the pan. Cook for a further 3-4 minutes.
Add the turmeric to the pan and stir. Peel and finely chop the potato and add to the pan. Rinse the red lentils in a sieve, then add to the pan followed by the stock.
Bring the soup to the boil and cook for 20-25 minutes until the lentils are soft.
Add the spinach/kale (removing any large stalks), cook for a further minute, then taste and season well with salt and black pepper as required.
At this point you can use a blender or hand blender to blitz the soup to a smooth purée, or use a potato masher to break up any large chunks of vegetable, or just leave it as a chunky soup. Stir through the dairy-free milk and the juice of the lemon, then serve. The soup freezes well so you can make a large batch whilst your at it and portion it up for the freezer.