Heat the oil in a large pan. Add the onion and cook over a low heat, stirring often, for about 10 minutes until the onion is soft.
Add the garlic and turmeric and cook for a couple more minutes.
Add the lentils, vegetable stock, mint, frozen spinach, bay leaf and thyme. Bring up to a simmer and cook for 20 minutes, stirring every now and again.
Add the butter beans and season generously with salt and pepper. Simmer for another 5-10 minutes then check the seasoning and serve.
