Rinse the lentils under cold water and set aside.
In a large pot or Dutch oven, heat the olive oil over medium heat. Add the chopped onion and sauté for about 5 minutes until softened.
Add the minced garlic, diced carrots, and celery to the pot. Cook for another 5 minutes until the vegetables start to soften.
Stir in the ground cumin and paprika, cooking for an additional minute until fragrant.
Add the rinsed lentils, diced tomatoes (with juice), vegetable broth, salt, and pepper. Bring to a boil.
Once boiling, reduce the heat to low and cover the pot. Let the soup simmer for 25-30 minutes or until the lentils are tender.
Taste and adjust seasoning with salt and pepper as needed.
If desired, garnish with fresh parsley before serving.