Cut the Maultaschen dumplings in half and chop into bite-sized pieces.
Cut the onion into fine cubes.
Heat a pan over medium-high heat. Add the chopped Maultaschen and onion cubes, frying for 3–4 minutes until lightly browned, stirring occasionally.
Whisk the eggs with salt and pepper in a bowl.
Pour the whisked eggs into the pan. Stir constantly like you're making scrambled eggs, for 2–3 minutes until cooked through.
Choose one method to finish: Pan method – Add the grated Emmentaler cheese and fold in gently for about 1 minute until melted. Baking method – Transfer the mixture to a baking dish, sprinkle the grated cheese on top, and bake at 180 °C (350 °F) for 10–12 minutes until eggs are set and cheese is melted.