In a large saucepan or pot, heat the olive oil over medium heat and cook the onion until translucent, about 5 minutes.
Add the garlic, ginger, paprika, turmeric, and ground cardamom. Cook for about 3 minutes until fragrant. Stir in the tomatoes with their juices and cook for another minute.
Add the red lentils and water. Cover and bring to a boil. Once boiling, reduce to a simmer. Cook covered until the lentils are fully pureed, stirring occasionally, about 25 minutes. Add the kosher salt and black pepper. For additional heat, add several pinches of cayenne.