Wash and scrape the mussels thoroughly under cold running water and remove the beards. Put the mussels in a pan, without any water, and heat until the shells open. (Any that remain unopened must be discarded.) Discard the empty shells, and loosen the mussels from the other shells. Arrange the mussels, in the bottom shell halves, in a cooking tray. Mix together the bread crumbs, parsley, garlic, chives, olive oil, salt and pepper. Spoon the mixture over each mussel and leave for about half an hour before cooking.
Put the mussels under a preheated broiler for just a few minutes to brown the crumb mixture and form a crust over the mussels. Try not to overcook.