“I cook all of the vegetables directly in the coals to get a really nice blister and char,” says chef Justin Smillie. “Ultimately at the end, all of the char on the skin will become a good portion of the vinaigrette.”
Light the grill: Place a chimney starter on the grate of a charcoal grill. Add newspaper in the bottom, then fill the top with charcoal. Light the newspaper; the fire will light the charcoal. When the charcoal is mature with ashed-over gray embers (about 30–45 minutes later), pour the charcoal from the chimney into the bottom of the grill. Set the grill rack aside—you won’t need it for this recipe.
Roast the vegetables and make the vinaigrette: Place the eggplant, leeks, zucchini, peppers, tomatoes, and garlic scapes directly onto the coals in an even layer. Stand the bunch of spring onions up so the bulbs are in the coals and the stalks are leaning against the side of the grill (this will create a natural handle for easy removal). Cook 10–15 minutes, turning the vegetables once to ensure they char evenly. Meanwhile, make the vinaigrette: In a mortar, combine the capers, anchovies, shallots, a big pinch of salt, and pepper. Using the pestle, crush and grind the mixture to break it down to a chunky mash. Transfer to a large bowl; stir in the vinegar and olive oil to saturate and combine. Season with lots of black pepper. Set aside.
Finish roasting the vegetables: The vegetables are done when they’re charred and soft. The tomatoes will be done first, followed by the leeks, peppers, zucchini, eggplant, and spring onions. Remove the tomatoes and add them directly into the vinaigrette; crush them with the back of a spoon to release juices. Chop the onions into fourths, discarding the charred stalks, and add to bowl. Chop the eggplant into chunks, add to bowl, and stir to combine; the eggplant will start to absorb the oil. Add the chopped celery and leaves; then chiffonade all the herbs, add them to the bowl, and stir thoroughly. Chop the zucchini and add to the bowl. Chop the peppers, discarding the seeds but keeping the charred skin, and add to the bowl. Stir while the vegetables are still hot so they will absorb all of the vinaigrette. Season to taste with more salt and pepper.
Assemble the caponata: Cut the bread into big chunks and place on the coals to toast for a few minutes until lightly charred. Cut the mozzarella into rustic pieces (or tear by hand) and place on a serving platter. Arrange the caponata next to the mozzarella, hand-tear the toasted bread, and add it to the platter. Finish with a drizzle of olive oil and serve.