Separate the greens from the Swiss chard ribs (or better still, just use the leafy green parts). Cut the chard leaves into 1 cm strips. Rinse the chopped chard well in cold water 2 or 3 times. This is an important step, as it removes the acidity from the chard. Drain carefully.
Cut the onion into small cubes and let it brown in a pan with a generous amount of olive oil.
In a bowl, beat the eggs, and add the cheese, the chard, and the cooked onion. Add salt and pepper.
Generously oil a non-stick pan (even one with a non-stick base) with two tablespoons of olive oil and heat over a moderate flame. Pour in the mixture and cook over low heat, pressing down well with a wooden spatula to obtain a thickness of 2 to 3 centimetres (about 1 inch) thick (the volume of the chard will decrease by half as it cooks).
This is the tricky part of the recipe: the truccha must not stick to the pan’s surface and should have a nice colour. After 20 minutes, when the top of the truccha starts to set, flip it over with a serving dish.
Oil the pan again and cook for 15 minutes on medium heat without a lid.