Heat a large saucepan or small stockpot over medium to medium-high heat. Once hot, add the oil. When oil starts to shimmer, stir in the onion, celery, and carrot. Cook for 8 minutes, stirring occasionally. Stir in garlic and cook for 2 minutes more, stirring occasionally. Add the potato, lentils, and vegetable broth. Turn up heat to medium-high and bring to a boil. Then turn heat down to medium-low and stir in cumin, ancho chili powder, black pepper, cayenne pepper, and turmeric. Cover and simmer until all the vegetables are very tender, about 40 to 50 minutes.

Using an immersion blender, carefully puree the soup right in the pot, until no chunks of vegetables remain. Or carefully transfer hot soup, in batches, to a blender to blend until smooth - and then return the soup back to the pot. Stir in lemon juice. Taste test and season with salt, if needed.  

To serve, ladle hot soup into individual bowls and serve with fresh lemon wedges to squeeze over the top. If desired, offer plain Greek yogurt and chopped cilantro for added flavors, plus warm pitas or flatbread for dipping.