Mix together mayonnaise, basil, salt, McCormick® Garlic Powder, and lemon zest in a small bowl. Set aside.
Cut off the top of the sourdough loaf and set aside. Use your fingers to pull out the bread inside to create a bowl. (Save the inner bread for making bread crumbs). Spread the basil-garlic spread along the inside of the bread and on the inside of the bread lid.
Begin layering ingredients inside the bowl. Start with 2 slices of ham. Cover with fresh mozzarella slices. Make sure to create an even layer that fully covers the inside of the mozzarella slices. Make sure to create an even layer that fully covers the inside of the bread bowl. Top with a layer of roasted red pepper slices, another 2 slices of ham, and a layer of tomatoes.
Sprinkle the tomatoes with salt and pepper. Scatter red onion and olives on top. Place bread lid on the sandwich to close.
Wrap the sandwich in plastic wrap. Place a heavy pot or large can on top of the sandwich and let sit for 2 hours. Unwrap, slice, and serve!