In a medium saucepan, bring beef broth to a boil. Add onion and garlic powder, ketchup, minced garlic and sliced onion.
When broth comes to a rolling boil, drop in the separated sliced roast beef and remove immediately from heat. Using a slotted spoon, remove roast beef from broth after 2-3 minutes. Return broth to stove on high setting and sprinkle Wondra flour over surface, stirring briskly to avoid lumps.
Simmer over medium heat 5 minutes. At the last minute, drain the sliced mushrooms and add. Pour over roast beef on white bread or buttered and toasted buns or bulkie rolls. Top with a thin slices of tomato or a few lettuce leaves , if desired. Season to taste with salt and pepper.
Serve.
