In a large soup pot, heat 2–3 tablespoons of water over medium heat. Add the diced onion and sauté for 3–4 minutes, stirring occasionally, until softened and translucent. Add more water if needed to prevent sticking.
Stir in smoked paprika and oregano. Cook for about 30 seconds to 1 minute, stirring constantly, to release their aromas.
Add the diced carrots and celery to the pot. Cook for about 2 minutes, stirring occasionally, to allow the vegetables to begin softening.
Stir in the minced garlic and cook for another 1 minute, stirring frequently to prevent burning.
Add the lentils, crushed tomatoes, and broth to the pot. Stir well to combine.
Bring the mixture to a boil, then reduce the heat to low. Cover the pot and let the soup simmer gently for 25–30 minutes, or until the lentils are tender.
Once the lentils are cooked, taste the soup and season with salt and pepper as desired. If using sherry, stir it in at this stage and let the soup simmer for another 2–3 minutes.
Ladle the soup into bowls and serve hot. Pair with crusty bread or a fresh green salad for a hearty meal.