In 2-quart saucepan, heat canola oil over medium heat. Whisk in flour until blended and continue stirring until roux is lightly browned and develops nutty aroma.
Whisk in broth, optional salt and onion powder. Bring to a gentle boil until just thickened, stirring. Cook and stir for 1 minute. Remove from heat and season with pepper. Add softened mushrooms and any soaking liquid.
Purée gravy in food processor or food mill. Return mixture to saucepan. Heat just to a simmer.