Heat the oil in a medium-size skillet. Add the onion and sauté over medium heat until golden.
Add the celery and mushrooms to the skillet and continue to sauté until the mushrooms are wilted and the onions are lightly browned.
Place the bread cubes in a large bowl. Sprinkle in the optional nutritional yeast, seasoning blend, sage, and rosemary and stir together until evenly coating the bread cubes.
Drizzle the broth over the bread cubes, a bit at a time, stirring the mixture up several times. The bread should be moist, but not drenched. Stir in the chopped nuts, optional dried fruit, then season with salt and pepper.
Transfer the mixture to a 2-quart baking dish and bake for 30 to 40 minutes, or until nice and crusty on top and on the sides. Serve hot.