Chop toasted bread into chunky breadcrumbs or pulse in food processor.
Remove the stalks from the portobello caps, chop and set aside.
In a bowl, combine the toasted breadcrumbs, chopped mushroom stalks, white onion, parmesan, garlic, parsley, Desert Dust and olive oil until evenly mixed.
Place the portobello mushroom caps on a lined and greased baking sheet with the gills facing up.
Spoon the dusted breadcrumb mixture into the portobello mushroom caps and gently pack into a dome shape.
Bake on the center rack for 25-30 minutes or until golden brown.