Herring wash, peel, remove the head and tail, cut in half. Taking refractory glass shape (or any shape), put herring. Cut onion into half rings, put on top of herring, salt, add seasoning. On top pour a mixture of mayonnaise and water (1:10). Cover, put in preheated oven to 220 degrees. for 30 minutes, then remove the lid and 10 minutes. The same dish can be cooked in the microwave, then 20 minutes.