Bring a large pot of salted water to a boil, then blanch carrots until tender, about 5 minutes. Drain carrots and set aside.
Combine tomato soup, olive oil, Worcestershire sauce, vinegar, mustard, and sugar in large pot and bring to a simmer while stirring to melt sugar. Remove from heat and set aside for about 5 minutes to let cool, but marinade should remain warm.
Mix together blanched carrots, green peppers, and onions, then pour marinade over vegetables. Let cool on counter, then place in fridge overnight.
Serve cold with a slotted spoon.