Mince half of the onion and slice the other half. Slice mushrooms. Microwave minced onion for 1 minute at 600W, drain and cool.

Mix breadcrumbs and milk in a bowl to moisten.

Combine ground meat, minced onion, salt, and pepper in the bowl. Mix until sticky, then divide into two portions and shape into patties.

Heat salad oil in a pan over medium heat. Cook patties for 2 minutes per side until browned. Add sliced onion and mushrooms to the pan and sauté until softened.

Add beef stew roux and water to the pan. Stir until thickened, then cover and simmer on low heat for 7–10 minutes, occasionally spooning sauce over patties.