Heat olive oil in a large pot over medium heat. Add diced onion and sauté until translucent, about 3-4 minutes. Add minced garlic and cook for another minute until fragrant.
Stir in diced carrot and celery, and cook for 5 minutes until they begin to soften.
Add rinsed red lentils, diced tomatoes (with their juices), ground cumin, ground coriander, turmeric, paprika, salt, and pepper. Stir everything together and cook for 2 minutes to let the spices bloom.
Pour in the vegetable broth and bring the mixture to a boil. Once boiling, reduce the heat to low, cover the pot, and let the soup simmer for about 20-25 minutes or until the lentils are tender.
Once the lentils are cooked through and the vegetables are soft, use an immersion blender to blend the soup until it reaches your desired consistency. You can also transfer a portion of the soup to a blender and blend until smooth, then return it to the pot.
Taste and adjust seasoning if needed. If the soup is too thick, you can add more broth or water to reach your desired consistency.
Serve the vegetarian red lentil soup hot, garnished with fresh cilantro or parsley if desired. Squeezing a bit of lemon juice into each bowl before serving adds an extra burst of flavor.
This vegetarian red lentil soup is hearty, flavorful, and perfect for a comforting meal!