Finely chop the onion and garlic.
Heat the oil in a casserole dish and gently cook the onion until soft. Add the garlic and fry for another minute then add the curry powder. Stir for a minute or so then add the chopped tomatoes.
Drain the lentils and chickpeas and stir into the curry. Season to taste.
Bring to the simmer and cook gently for 10 minutes under cover.
Rinse and drain the spinach then add it to the curry. Put the lid on, turn off the heat and let the spinach wilt in the steam - this should only take a couple of minutes. Then stir well to mix everything together.