Brush the large saucepan with oil. On medium heat, stir onion for 2-3 minutes without browning. Add curry powder and cumin and stir for about 1 minute. Add tomato and stir well, then add rinsed lentils. Cover with water and bring to boil.
Cover pan and simmer until lentils are almost cooked (20-35 minutes), adding a little more water during the cooking if necessary.
Meanwhile, wash spinach 2 or 3 times in a large quantity of cold water. Add drained spinach to lentils. Cover pan and cook for a few minutes or until spinach has softened. Season with chilli paste (optional) and serve with bread.