Slice the bread, sandwich style (the whole thing) and scoop out most of the soft middle. You can save the soft middle for breadcrumbs or something else.
Cook the mushrooms in a pan with the olive oil and garlic. Cook them until they're soft then remove and lay on a towel to soak up any extra moisture.
Slice the walla walla sweet onion in about 1/4 inch slices and sautee until soft and brown. Set aside for a bit.
Spread the olive 'spread' that you have either bought or made onto both sides of the hollowed out bread.
Lay the roasted red peppers over top of the 'spread'. ps... if you want the 'spread' recipe, I can post that too :)
Top peppers with the portabellos that you cooked and on top of that, pop on the onions. Sometimes I'll put a little salt and pepper on top.
Close up your little masterpiece and wrap it TIGHTLY in saran wrap. The point is that you want it to get smashed down. I wrap it up and then put it in the fridge with my LeCreuset on top, to smash it down. Let it go for a while... 1/2 hour or so. Pull it out, slice it and enjoy! yummm :) (note: this is why you want to make sure extra moisture is out of the mushroom... if you don't, your bread will get soggy from the 'smashin'')