Ingredients: 
1/2 pounds beef round, cut thin and fat trimmed 
1/4 cup olive oil 
2 tablespoons balsamic vinegar 
1 teaspoon dried oregano 
2 garlic cloves, smashed to pulp 
1/4 teaspoon red-pepper flakes 
1/4 teaspoon salt 
1/8 teaspoon freshly ground black pepper 
Filling: 
3 tablespoons olive oil 
1/4 cup finely chopped onion 
1/2 cup bread crumbs 
2 large hard-cooked eggs, shelled and chopped 
2 ounces prosciutto (or ham), coarsely chopped 
2 tablespoons freshly grated Parmesan cheese 
2 tablespoons chopped fresh flat-leaf parsley 
1 garlic clove, finely minced 
1/2 teaspoon salt 
1/4 teaspoon freshly ground black pepper 
1 (16-ounce) jar marinara sauce (or your own) 
1 pound spaghetti, cooked according to package directions 
Additional freshly grated Parmesan cheese for garnish