For dressing, in a small saucepan, stir together tomato soup, vinegar, salad oil, and sugar. Bring mixture just to boiling. Remove from heat; cool, stirring occasionally. Pour into a mixing bowl; beat with rotary beater or an electric mixer on low speed until smooth.
In a large mixing bowl, combine the frozen or fresh carrots, the green pepper, and chopped onion. Pour dressing over vegetables. Stir gently to coat. Cover and chill for 2 to 24 hours. Serve the salad with a slotted spoon. Makes 8 side-dish servings.