Slice the king oyster mushrooms and cut the spring onions into rings. Remove the seeds from the pepper and dice it. Preheat the oven to 100°C (top and bottom heat). Whisk the eggs in a bowl and season well with nutmeg, salt and pepper. Heat 1 tbsp. oil in a frying pan and briefly fry approx. 1/4 of the mushrooms, the diced pepper and the white parts of the spring onions. Pour 1/4 of the egg mixture over the top and leave to set over a low heat for approx. 8 minutes. Flip using a flat plate and cook for a further 5–7 minutes until done. Keep warm in the oven. Prepare three more frittatas using the remaining ingredients. Arrange 3 slices of bresaola on each frittata and sprinkle with the green parts of the spring onions.