Combine vegetables, onion, thyme and water in a saucepan. Bring to a boil, reduce heat and simmer, covered, until vegetables are very tender, about 8-10 minutes. Remove from heat, stir in butter and cheese. Blend smooth in a blender or food processor and add salt, pepper and lemon juice to taste. Soup will be thick. Per Cup: Calories: 70, Protein: 4g, Carbohydrates: 7g, Fat: 4g, Saturated Fat: 2g, Cholesterol: 9mg, Sodium: 142mg, Fiber 2g.