Chop all your vegetables into small, even pieces for quick cooking.
Crack the eggs into a bowl, add salt and pepper and whisk until smooth.
Heat oil or butter in a non stick pan on medium flame. Add onions and bell peppers first, saute for 2-3 minutes until slightly soft.
Toss in the tomatoes, cook for another 1-2 minutes.
Spread the veggies evenly in the pan and pour the beaten eggs over them.
Let the eggs cook on medium heat without stirring, until the edges start to set.
Sprinkle grated cheese eveny on top of the omelette.
Once the cheese melts and eggs are fully cooked, fold the omelette in half, slide onto a plate and enjoy.