Cook the macaroni according to their package directions. Drain well and then set aside to keep warm.
In a medium saucepan, combine the carrots and cauliflower. Add water to cover and bring to a boil. Reduce the heat and simmer for 15 minutes, until tender. Drain well and then set aside to keep warm.
Separately, sauté the onion in the margarine for roughly 2 minutes, or until tender. Add the flour, stirring until combined. Stirring constantly, cook for 1 minutes. Gradually add the milk, and then cook over medium heat until the mixture is thickened and bubble, stirring continuously.
After reducing the heat to low, stirring constantly, add the cheese, Worcestershire sauce, salt, and pepper, and cook until the cheese melts.
Next, add the pasta and cooked vegetables to the cheese sauce and stir gently to coat well. Continue to cook over low heat, stirring gently, until heated thoroughly and ready to serve.