Add the oil to a large deep fry-pan and turn heat onto low.
Once the fry-pan is hot, sauté onions, garlic and ginger for five minutes or until the onions are soft. Add the curry powder and veggies and sauté for another two minutes.
Add the tinned tomatoes, coconut milk and cubed tofu (if using), and mix well. Bring to a boil, then reduce the heat to a low and simmer for 15 minutes, stirring occasionally.
Open tin of lentils. Drain liquid and rinse. Add to curry, along with the spinach. Mix, and then simmer for another 5 minutes.
Add the juice of ½ lemon (reserve the other half to serve as wedges with your curry on the side) and season with salt and pepper to taste. Mix well, taste test and adjust with extra salt or lemon juice if needed - the salt and lemon juice will bring it all alive.