In a medium saucepan, heat the oil over medium heat. Add in the onions, carrots and garlic, and cook until fragrant, around 2-3 minutes.
Mix in the lentils, cumin and red pepper flakes, and cook for an additional 1 minute.
Add in the water, tomato paste, salt and pepper. Reduce heat and allow to simmer for around 30 minutes.
Transfer to a blender and blend until smooth. Add in additional water if it is too thick, until the soup reaches your desired consistency.