Peel the onion and then slice it 1/8 inch thick on a mandolin slicer or with a sharp knife. Then chop the thin slices into a small dice. Put in a large mixing bowl.
Add the rest of the ingredients to the bowl and mix well. Take the time to make sure everything is thoroughly combined.
Spread the dip in a shallow baking dish, and even it out. Bake for about 30-40 minutes until bubbling and hot throughout. You can put it under the broiler briefly for more browning if you want.
While the dip is baking, heat a grill pan on high until very hot and grill the slices of bread until lightly charred on both sides.
Serve the dip hot out of the oven, with the bread.