Preheat a grill or grill pan to medium-heat. Lightly brush the eggplant, zucchini, bell pepper, portobello (read the description, maybe you have to slice it after it's grilled) and red onion with 1/4 cup of olive oil. Season with salt and pepper. Cover and grill, turning once, until charred, about 6 minutes.
Using a food processor, puree the spinach, pine nuts and parmigiano-reggiano; season with salt and pepper. With the machine one, drizzle in the remaining 1/4 cup of olive oil. Transfer the pesto to a bowl. Rinse the food processor.
Using the food processor, pulse the giardiniera and olives into a coarse relish.
Slice the top quarter off the bread and scoop out the insides. Spread half the pesto on the inside of the bread, layer with half of the grilled vegetables, then spoon the remaining pesto on top. Fill the bread with the remaining vegetables and top with the provolone. Spread the inside of the bread top with the vegetable relish and set into place. Press down firmly, then cut into wedges.