Lightly whisk the eggs in a small bowl. Stir in two pinches of salt and set aside.
Thinly slice the pepper and the onion.
Heat the oil in a frying pan. Add the onion and pepper and gently sauté, over low heat, until soft. Add a pinch of marjoram and the balsamic vinegar, then stir until the onion and red pepper have caramelized.Transfer the mixture to a plate.
Clean the pan with kitchen towels (or use a pancake pan), then add a small spoonful of oil.
Pour in the eggs, letting the mixture spread put evenly.
When it’s half cooked through, crumble the cheese all over it.
Cover with a lid, turn off the heat, then gently cook for about 3 minutes, or until the top of the omelette has just set.
Spoon the caramelized onion and red pepper over half of the omelette, scatter some fresh herbs on top and season with salt & pepper. You can add a pinch of chilli flakes too.
Fold the omelette in half. Cook for a few seconds, then slide it to a plate.
Serve warm.