In a food processor, pulse the artichokes, peppers, olives, 3 tbsp. EVOO and the oregano to a coarse puree; season. Hollow out the top of the loaf, leaving a 1 1/2-inch border; drizzle with the remaining 1 tbsp. EVOO. Spread half the artichoke tapenade on the bread bottom. Add the meats and cheese, the remaining tapenade, onion slices and bread top. Press down to compact. Wrap tightly in plastic, then foil, crimping the edges to seal. Refrigerate at least 4 hours. Cut into wedges.