Keep it simple by preparing just about everything ahead of time.
Cover a large (12-by-18-by-2-inch) baking pan with parchment; dust lightly with cornmeal. On a floured surface, combine dough and form a long, curvy snake shape; place on pan. Push two olives into head for eyes. Cut V-shaped scales down back. Brush dough with oil. Cover with plastic wrap and let rise until doubled in size, about 1 hour. Preheat oven to 350°F. Bake until crust is golden, 30 to 40 minutes. Cool in pan on rack.
Remove roasted peppers from jars and set aside. Add olive oil to oil from peppers to make 1 cup. Combine oil, celery, olives, capers and red pepper flakes in a small bowl.
Slice loaf horizontally. Place bottom half on tray; arrange arugula leaves on it. Layer on prosciutto and mozzarella, top with roasted red peppers. Spoon on olive relish and replace top.
Cut a forked tongue shape from red pepper and place at head.