Heat 2 tablespoons olive oil in a Dutch oven or large pot over medium heat until shimmering.
Add 1 diced medium yellow onion, 2 peeled and diced medium carrots, and 2 diced medium celery stalks. Cook, stirring occasionally, until the onion is softened, about 5 minutes.
Stir in 3 minced garlic cloves, 1 tablespoon tomato paste, 2 teaspoons kosher salt, 2 teaspoons ground cumin, 1 ½ teaspoons smoked paprika, and ¼ teaspoon black pepper. Cook, stirring occasionally, until fragrant and the tomato paste is darkened in color, 1 to 2 minutes.
Stir in 6 cups low-sodium chicken broth and 1 ½ cups dried red lentils. Bring to a simmer over medium-high heat.
Reduce the heat to low, cover, and simmer until the lentils are tender, 15 to 18 minutes.
If desired, for a creamier soup, blend with an immersion blender directly in the pot, or transfer to a blender to blend to your desired consistency.
Taste and season with more kosher salt as needed. Garnish with chopped fresh parsley leaves if desired.
