What to do:

Rinse lentils under cold water in a strainer with fine mesh and set aside.
Wash and prepare vegetables. Chop bell pepper, onion, carrots, and potatoes into bite-size pieces. Dice celery and mince garlic. Set potatoes aside for later.
Heat 1 Tbsp. olive oil in a medium pot over medium heat. Add celery, peppers, onions, and carrots. Cook about 7 minutes, stirring occasionally, until vegetables begin to soften.
Add garlic, salt, black pepper, paprika, and cumin. Cook about 30 seconds until fragrant. Stir in tomato sauce and simmer 2–3 minutes.
Add chicken broth, water, and lentils. Bring to a boil, then reduce heat to medium-low, cover, and simmer about 25 minutes, stirring occasionally, until lentils are almost tender.
Stir in potatoes, cover, and cook 15–20 minutes until potatoes are tender.
Transfer ½ cup soup to a blender and blend until smooth. Stir the puréed soup back into the pot to thicken the broth.
Divide soup into bowls, garnish with fresh parsley, and serve.