To Make Olive Salad: Place giardiniera, green and kalamata olives, capers, garlic, oregano, crushed red pepper and 1/3 cup olive oil in a food processor. Pulse to combine, without over-blending. Set aside. Can be made several days in advance.
To Prepare Vegetables: Trim ends and peel eggplant, then cut into 1/4-inch rounds. Trim ends from zucchini. Cut in half lengthwise, then cut into 1/4-inch strips. Stem and seed bell peppers. Remove stems from portobello mushrooms. Brush all the vegetables with olive oil and sprinkle with coarse salt. Grill vegetables in batches over medium heat until charred or browned. Allow the skin from the peppers to char until blackened. Place cooked vegetables on a large plate. When peppers are cool enough to touch, remove blackened skin and return to the plate with the other vegetables. Slice the portobello into thick strips.
To Make the Muffuletta: Cut the loaf of bread in half horizontally. Hollow out the two halves of the bread and reserve the extra bread for another use.
Spread the olive salad on both halves of the bread. Layer grilled vegetables, beginning with the bottom half, until they are gone. Use artichoke hearts and pepadew peppers as the final layers and cover with the top of the bread.
Place the bread on a plate and cover with another plate. Rest something heavy on top for several hours or overnight, like cans of tomatoes, to press the layers together. Serve chilled or at room temperature, cut into wedges.