Rinse the red lentils.

Heat the olive oil in a large pot over medium heat. Add the chopped onion and cook until softened, about 5 minutes.

Add the rinsed lentils, water or stock, cumin, paprika, and black pepper to the pot. Bring to a boil, then reduce heat and simmer for 20-25 minutes, or until the lentils are soft.

Use an immersion blender or regular blender (carefully!) to blend the soup until smooth. If using a regular blender, blend in batches.

Season with salt to taste. Serve hot with a squeeze of lemon juice, if desired.