A stromboli is kind of a cross between a grinder and a calzone. Bread dough is rolled out, filled with sliced meats, cheeses and vegetables, then rolled up into a tube and baked.
To serve, stromboli are simply sliced like a loaf of bread, creating a spiral baked sandwich that is perfect for large parties. If you like, you also can serve sandwich condiments (or even warmed marinara) alongside the stromboli slices for dipping. We've offered suggestions for fillings; but mix and match to suit your group (or devise your own combination).
Just be careful with vegetables. Because you will be baking the fillings in the dough, watery vegetables (such as tomatoes) can release too much liquid during cooking. To avoid this, cook most vegetables in a skillet before adding them. Sun-dried tomatoes would be a good alternative to fresh.