In the bowl of a food processor, combine the basil, parsley, garlic, vinegar, mustard, salt and pepper. Blend to a coarse paste. With the motor running, slowly add the olive oil and blend until smooth. (You can also make this with a mortar and pestle if you prefer.)
Assemble the sandwich:
Lay the bread on a large cutting board. Use a large, sharp, serrated knife to carefully slice it in half, like cutting a cake into layers. Drizzle and spread all of the vinaigrette evenly over the two cut halves of bread.
Layer the sandwich components evenly over one half of the bread, sprinkling each layer with a bit of salt and pepper, in this order:mozzarellatomatoesavocadoonionarugula
Drizzle a bit of olive oil over the arugula, then top with the other half of the bread.
Wrap the sandwich snugly in aluminum foil and place it on a small, rimmed baking sheet to catch any drips. Place it in the refrigerator and set something heavy on top (I use a few cast iron skillets). After an hour or two, flip the sandwich over and continue pressing it for a total of 4 - 24 hours.
Grill the sandwich:
If you have a grill or griddle large enough to accommodate the whole sandwich, leave it whole. Otherwise, unwrap it, place it on a large cutting board, and use a large chef's or bread knife to cut it in half crosswise.
Coat a wide skillet with a thin layer of olive oil. Place it over a medium flame until the oil shimmers, then add one sandwich half. Top the sandwich with a piece of foil and place something heavy (yet heat-prooon top of it (I use another cast iron skillet). Cook on the first side until the bread is crisp and golden, a minute or two. Flip the sandwich and heat and press it on the second side until golden and crisp, another minute or two.
Return the sandwich to the cutting board, cut into pieces, and devour immediately. Repeat with the other sandwich half (or save it in the fridge for up to 2 days to toast when ready to serve).
Inspired by Local Flavors and Ham Pie Sandwiches.We like this giant sandwich best after 24 hours of pressing, when the bread has absorbed the juices from the tomatoes but the filling is still fresh. However, the un-toasted sandwich will keep in the fridge for up to three days; the filling components hold up surprisingly well.Feel free to go wild with the filling; goat cheese, grilled sweet peppers, eggplant, and zucchini would all be superb additions.Nutritional values are based on one of four large sandwiches.