Rinse and chop the tomato, onion, and green pepper into small, even-sized pieces.

Lightly spray a large frying pan with cooking spray.

Heat the pan over medium-low heat.

Pour the egg substitute or beaten egg whites into the heated frying pan.

Evenly distribute the diced tomato, onion, and green pepper over the egg mixture.

Sprinkle the shredded fat-free cheddar cheese over the vegetables.

Cover the frying pan.

Cook until the top of the omelette appears to be getting dry and the cheese is melted.

Carefully flip the omelette using a spatula.

Cook for another minute or two until the omelette is fully cooked and set.

Slide the omelette onto a plate.

Serve immediately and enjoy!