Preheat oven to 350 degrees Fahrenheit (175 degrees Celsius).
In a medium mixing bowl, combine the ground beef, breadcrumbs, egg, milk, salt, pepper, and garlic powder until just incorporated.
Shape the beef mixture into 6 thick, oval-shaped patties.
Heat vegetable oil in a large skillet over medium-high heat and sear the patties for 3 minutes per side until a brown crust forms.
Transfer the seared patties to a 9x13-inch baking dish in a single layer.
Arrange the sliced onions evenly over the top of the meat patties.
In a separate bowl, whisk together the cream of mushroom soup, cream of chicken soup, and beef broth until smooth.
Pour the soup mixture over the patties and onions in the baking dish.
Cover the dish tightly with aluminum foil and bake for 30 minutes.
Remove the foil and continue baking for an additional 15 minutes until the gravy is bubbling and the meat reaches an internal temperature of 160 degrees Fahrenheit.