Heat 1/4 cup olive oil in a large pot over medium heat. Cook and stir carrots, onion, salt, parsley, black pepper, ginger, tarragon, and cumin in the hot oil until the onion is translucent, 5 to 7 minutes.Stir lentils and tomatoes into the carrot mixture. Pour vegetable broth over the vegetables, stir, and bring to a boil. Reduce heat to low, place a cover on the pot, and simmer until the lentils are tender, 45 to 50 minutes.Stir spinach and zucchini into the broth mixture, simmer until the zucchini is tender, about 7 minutes more. Remove pot from heat and season soup with salt. Drizzle 1 teaspoon olive oil over the soup before serving.