Preheat oven to 450 degrees.
In a large pot, steam the mussels over 2 cups water, covered until open, about 5 to 6 minutes. Remove half shell and lay flat on a cookie sheet.
Cube prosciutto into 1/4-inch dice and place in bowl. Place mint, basil, oregano, oil and garlic into blender. Process until smooth. Remove and pour into bowl with prociutto. Add breadcrumbs and tomato sauce and mix well.
Pack each mussel and shell full with green mixture. Bake 8 to 10 minutes, until lightly golden brown on top and serve.