Add the onion to a large pan with the olive oil and sauté for 10 minutes on a low heat. Add in the spices, garlic & ginger and fry for a further few minutes.
Thoroughly wash & drain the lentils.
Next, add the lentils, water, veg stock cube and the tomatoes to the pan and simmer for 20 minutes on a low heat.
Finally, squeeze in the lemon juice and season with salt & pepper.