In a large soup pot, heat the oil over medium-low heat. Thinly slice the leeks and add them to the pot along with the onion. Cook, stirrinig, until the vegetables wilt, about 5 min. Add the carrots, celery, lentils, peas, beans, thyme, pepper, and broth. Bring to a boil. Reduce the heat and simmer, covered for 45 minutes stirring occasionally. Stir in the tomatoes and continue to simmer, covered, for another 15 minutes, until the white beans are tender. Stir in the spinach and simmer, uncovered, until wilted, about 3 minutes. Ladle into soup bowls and serve.
Nutrition Information: Calories: 130; Fat: 3 grams; Protein: 9 grams; Carbs: 21 grams; Fiber: 5 grams, Cholesterol: 0; Sodium: 130 mg; Potassium: 120 mg