In a small nonreactive saucepan, bring the carrot juice and lemon juice to a boil over moderately high heat. Cook until the solids separate from the liquid, about 5 minutes, then strain into a bowl. Return the juice to the pan. Boil over moderately high heat until the juice is reduced to 2/3 cup, about 20 minutes. Transfer the mixture to a bowl and let cool slightly. Whisk in the rice wine vinegar, soy sauce, vegetable oil and chili oil and season with salt. Whisk in the scallion just before serving.
The dressing can be refrigerated, covered, for up to 3 days.
One Tablespoon Calories 31 kcal, Protein .6 gm, Carbohydrate 6 gm, Cholesterol 0, Total Fat .7 gm, Saturated Fat .1 gm.