Prepare the Ingredients:

Crack the eggs into a bowl. Add the milk or water, salt, and pepper. Beat the mixture until all the ingredients are well combined and the mixture is slightly frothy.

Stir in half of the chopped herbs into the egg mixture. Reserve the rest for garnish.

Cook the Omelet:

Heat the olive oil or butter in a non-stick frying pan over medium heat. Once hot, sauté the chopped onion until translucent and slightly golden, about 2 minutes (if using).

Pour the egg mixture into the pan. Let it sit for a few seconds until the edges start to set.

With a spatula, gently push the set edges towards the center, tilting the pan to allow the uncooked egg to flow to the edges.

Add Fillings:

Sprinkle the grated cheese over half of the omelet while the top is still slightly runny. Add the diced tomatoes over the cheese if using.

Continue cooking until the cheese starts to melt and the egg is set but still soft and creamy on top. Avoid overcooking to keep the omelet tender.

Fold and Serve:

Carefully fold the omelet in half with the spatula and slide it onto a plate.

Garnish with the remaining fresh herbs. Serve immediately for the best flavor and texture.