Sprinkle salt over carrots, celery, and onion. Heat 1 tablespoon oil in a large soup pot over medium heat. Cook and stir vegetables until onion is translucent, about 5 minutes. Push vegetables aside to clear a space in the center of the pot. Heat 1 tablespoon oil in the center. Sprinkle garam masala over the oil and toast for 1 to 2 minutes. Stir into vegetables until well coated.
Pour vegetable broth into the pot; bring to a boil. Reduce heat to medium-low and add farro. Cover and simmer until almost tender, about 20 minutes. Add lentils. Cover and simmer, adding more broth if needed, until farro and lentils are tender but not mushy, about 20 minutes. Season with salt.