In small saucepan over medium heat, cook dressing, carrots, onions, and peppers until tender. Stir in cucumber and tomatoes. Set aside; keep warm.
Beat together eggs, milk, and salt, if desired. In 7-to 10-inch omelet pan over medium heat, heat 1 teaspoon oil until just hot enough to sizzle test with a drop of water. Pour in 1/2 cup of the egg mixture. Mixture should set immediately at edges. With inverted pancake turner, carefully push cooked portion at edges toward center, tilting pan and moving cooked portions so uncooked portions can reach hot pan surface. When top is thickened and no visible liquid egg remains, fill with 1/4 of the vegetable mixture. Fold omelet in half. Invert onto plate. Repeat for remaining omelets.