Crack the eggs and place in a bowl. Add some salt (a pinch to 1/4 teaspoon) and beat until the texture becomes smooth. Set aside.
Heat the oil in a pan.
Saute the yellow onion and tomato.
Once the onion and tomato becomes soft. Add the bell pepper and scallions. Cook for 1 minute.
Pour-in the beaten egg. Spread the mixture over the pan. Cook in medium heat for 2 to 3 minutes or until the bottom part forms.
Flip the omelet to cook the other side. Note: you can put the omelet on a plate with cooked part facing down. Gently flip and slide the omelet from the plate to the pan. The cooked part should be facing up now.
Transfer to a serving plate. Top with shredded sharp cheddar cheese.