Heat the oil in a saucepan.
Add the onions, saute until the edges start to brown, then add the garlic.
Saute for a few seconds, then add tomatoes, coriander powder and cumin powder.
Saute until the tomatoes thicken and turn darker, about five minutes.
Add the lentils and stir to mix.
Add enough water to cover the lentils by half an inch. Bring to a boil, then cover with a tight lid, lower heat to a simmer, and cook until the lentils are really soft, about 20-30 minutes.
Stir in the spring greens and the Harissa paste. Add salt to taste. Bring to a boil and let the stew cook another five minutes.
Turn off the heat, add the mint and lemon juice, and check salt.
Serve hot with some couscous, bulgur, or brown rice.