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Place sliced tomatoes, onions, mozzarella, roasted peppers and capers, decoratively, on a large platter. Sprinkle the top with capers. Tuck the basil leaves decoratively in between things on the platter, allowing the top 1/3 of the leaves to be visible.
Place the arugula in a bowl and place toss with some of the shaved parmesan. Place another pile of shaved parmesan on top of the greens and place the bowl next to the filled platter, with tongs, so guests can help themselves. Accompany with a carafe of garlic confit oil, or regular extra-virgin olive oil and some balsamic vinaigrette. Always have some Kosher or sea salt and a pepper mill available, to season as needed.
The peppers can be roasted 2 days ahead and kept refrigerated, well covered.
The greens can be cleaned a day ahead and kept refrigerated, wrapped loosely in paper towels and placed into a large plastic bag.
The shaved parmesan can be accomplished early in the day and kept refrigerated, covered. Allow to come close to room temperature, for best flavor.
The garlic confit can be made a few days ahead and kept in the refrigerator, in a closed tub or jar.