Rinse the red lentils under cold water until the water runs clear.
Heat olive oil in a large pot over medium heat. Add the chopped onion and sauté until translucent, about 5 minutes.
Add the diced carrot and potato to the pot and continue to sauté for another 5 minutes, stirring occasionally.
Stir in the tomato paste and cumin, cooking for an additional 2 minutes until fragrant.
Add the rinsed lentils and the vegetable broth to the pot, bringing the mixture to a boil.
Once boiling, reduce the heat to low and cover the pot. Simmer for 20-25 minutes until the lentils are tender.
Remove the pot from heat and use an immersion blender to puree the soup to your desired consistency.
Stir in lemon juice and season with salt and black pepper to taste.
Serve hot, garnished with fresh parsley or a sprinkle of paprika if desired.