Heat Extra Melt via one of the methods located on pouch.
In medium stockpot, whisk cheese sauce, blue cheese crumbles and hot water. Heat to 165°F, stirring occasionally; some of the blue cheese will not fully melt. Hold warm.
To assemble hoagie, place 4 ounces meat into opened bun. Top with 2 ounces mushrooms and 1 1/2 ounces onions. Drizzle 2 ounces blue cheese sauce on top of hoagie.