In a medium saucepan, combine the vinegar, water, garlic, thyme, oregano, red pepper flakes, and salt. Bring to a boil and remove from the heat. Chop the cauliflower, carrot, and celery and toss with the oil in a medium bowl. Pour the hot brine over the cut vegetables and let cool to room-temperature, about 1 hour. Transfer to a sealed container and store in the refrigerator for up to 1 month.
In a small bowl, combine the sliced olives, chopped peppers, capers and parsley. Mix and season with salt and freshly cracked pepper. Transfer to a sealed container and store in the refrigerator for up to 3 weeks.
Spread a generous amount of olive relish on the top half of the bread and a followed by an equally generous amount of giardiniera on the bottom half. Layer the provolone, mortadella, salami, and hot soppressata on the bottom half of the bread. Close the sandwich and press down gently. Wrap the sandwich tightly in plastic and weigh it down with a cast-iron skillet in the refrigerator for 1-2 hours before serving. Slice into four pieces and serve.