Place bread cubes on large shallow baking pan and bake until golden, stirring occasionally, about 20 minutes. Transfer to large mixing bowl. Turn oven down to 350°F.
Melt butter in large heavy skillet. Add onions and cook until clear, stirring occasionally (about 10 minutes). Add red peppers, mushrooms and celery; cook until tender – about 5 to 7 minutes.
Combine with bread in mixing bowl; add nuts, seasonings, broth and beaten eggs. Stir well and pour into an 8” X 8” greased baking pan or one of similar size. (Can be prepared a day ahead and refrigerated). Cover and bake for about 1 hour.