Rinse the lentils under cold water until the water runs clear.
In a large pot, heat the olive oil over medium heat. Add the chopped onion and cook until translucent.
Add the minced garlic, ground turmeric, ground cumin, and ground coriander. Cook for another minute.
Add the chopped tomato and cook until it softens.
Add the rinsed lentils and water to the pot. Bring to a boil, then reduce the heat and let it simmer for about 20 minutes, or until the lentils are tender.
Stir in the chopped spinach and cook for another 5 minutes. Season with salt and black pepper to taste.