Preheat a large stock pot over medium-high heat and spray with cooking spray (or drizzle with olive oil). Sauté onions and carrots, stirring frequently, until they begin to soften, about 4-5 minutes.
1 medium onion, 2 carrots
Add potatoes, red lentils, cumin, salt and cayenne to the pot and continue sautéing for 2-3 minutes. Using a wooden spoon, stir tomato paste into the pot and cook for 1-2 minutes so that the paste can absorb the flavors of the other ingredients.
Pour in chicken broth, give the entire mixture a stir. Increase heat to high, bringing the soup to a boil. Reduce heat to low and simmer until potatoes and lentils are cooked through, 15-20 minutes.
4 cups chicken broth
Remove pot from the heat and add mint and lemon juice. Puree until smooth using an immersion hand blender. Check for seasoning and adjust accordingly before serving.
1 tablespoon dried mint, 2 tablespoons lemon juice
Notes
This soup tastes even better on days two and three so I love making extra for lunches later in the week. It also freezes great! If you don't have an immersion blender, you can transfer the soup to a blender or food processor.