Heat the olive oil in a large pot or Dutch oven over medium heat. Add the sliced onions and a pinch of salt. Cook, stirring occasionally, for about 15-20 minutes until onions are caramelized and golden brown.
Once the onions are caramelized, add the minced garlic, ground cumin, and smoked paprika. Stir for about 1-2 minutes until fragrant.
Add the diced carrots and cook for another 5 minutes until they start to soften.
Add the rinsed red lentils, vegetable broth, and diced tomatoes to the pot. Stir well and bring to a boil.
Once boiling, reduce the heat to low, cover, and let simmer for about 20 minutes, or until the lentils are tender.
If you prefer a smoother texture, use an immersion blender to blend the soup to your desired consistency. Otherwise, leave it chunky.
Stir in the salt, pepper, and lemon juice. Taste and adjust seasoning if necessary.
Serve hot, garnished with fresh parsley or cilantro if desired.
