1. Heat the oil in a large nonstick skillet over medium-high heat. Add the zucchini, artichoke and tomato. Cook 5 minutes, stirring occasionally, until vegetables are crisp-tender. Set aside.
2. Beat the egg whites with a hand mixer until they form soft peaks. Add the whole eggs, salt and pepper; stir.
3. Heat an 8-inch nonstick skillet over medium-high heat; add the egg mixture. Cook 2 to 3 minutes, or until lightly browned on the bottom.
4. Using a spatula, slide omelet onto a plate. Return it to the pan with the cooked side facing up; cook 10 to 12 minutes, until golden.
5. Place vegetable mixture and cheese on half the egg and fold it over to enclose the filling. Press down lightly with the spatula until it holds the shape and the cheese melts.