Clean and sanitize the mushrooms. Break out or cut the stem at the base and chop finely. Heat 2 tablespoons of oil in a large frying pan. Fry the mushrooms in it, possibly in portions on both sides for 4-5 minutes until brown, take them out and let them drain on kitchen paper.
Cut the ham into small pieces. Fry the ham in a hot frying pan for 3-4 minutes, turning, and remove. Peel and finely dice onions. Wash parsley, dab dry, pluck leaves from the stalks and chop finely.
Fry the onions, mushroom stems and parsley in a hot frying pan for 4-5 minutes, while turning, until all the liquid has evaporated. Stir in ham, season with pepper, let cool down a little. Clean, wash and drain the rocket.
Season the vinegar with salt, pepper and sugar, fold in 2 tablespoons of oil. Fill mushroom heads with ham and parsley mixture. Arrange rocket on small plates and sprinkle with vinaigrette. Arrange 3-4 stuffed mushrooms on each plate.