Vegan Salisbury Steak w/ Mushroom Gravy

Name: Vegan Salisbury Steak w/ Mushroom Gravy
Cuisine: American
Ingredients: 5 vegan burger patties; 3 Tbsp margarine; 8oz sliced baby bella mushrooms; 1/2 cup diced onion; 1/8 tsp garlic powder; 3 Tbsp flour; 1/8 cup dried minced onion; 1/4 tsp onion powder; 1/4 tsp garlic powder; 1/8 tsp celery seed; 1/8 tsp pepper; 1/4 tsp dried parsley; 1/4 tsp salt; 2 1/2 cups mushroom broth; salt; pepper; mashed potatoes