Clean and slice the mushrooms. Clean, wash and drain spring onions and cut into fine rings. Mix eggs, 1 tablespoon cold water, some salt, pepper and nutmeg
Heat the oil in a small, coated pan (approx. 16 cm Ø). Fry the mushrooms for 4-5 minutes while turning. Finally add 2/3 of the spring onions and fry briefly. Season with salt and pepper. Pour eggs evenly over the mushrooms and let them simmer covered at low heat for 15-20 minutes
Clean and wash the radicchio, drain well and cut into fine strips. When the frittata has set, sprinkle with cheese and cover and let it melt. Arrange the finished frittata with the radicchio and sprinkle with the remaining spring onions