Beard and clean mussels. Open mussels over bowl to collect liquid. Set aside.
Cut stale bread up into cubes, place in bowl and moisten with stock. Let stand until bread has softened. Squeeze bread to remove all liquid.
Put the beef, bread, parsley, garlic, Parmesan cheese, black pepper, salt and egg in a bowl and mix all ingredients until they are well blended.
Stuff mussels placing a heaping tablespoon of the stuffing on an open shell then press the two shells shut and wipe off the stuffing that squishes out.
Tomato Sauce: Sauté garlic, chilli and parsley in the oil over medium heat; do not let garlic brown. Add the crushed peeled tomatoes, stir and then add the mussel juice you've kept aside. Add salt and let sauce simmer for about 15 minutes.
Gently place mussels into saucepan, cover and let mussels stew for about half an hour or until stuffing has cooked through. Serve and garnish with sprinkling of remaining tablespoon minced parsley.