Beat the egg in a small bowl and add to the beef followed by the worcestershire sauce, salt, onion powder, garlic powder, and black pepper.
Add the bread crumbs then use your hands or a fork to gently bring everything into a cohesive mixture. Set the mixture aside while you heat your pan.
In a 10-inch or larger heavy skillet, add the oil and heat over medium 2 minutes. Form four patties approximately 1 1/2" thick and lay them in the pan 1 inch apart.
Let the patties cook on medium heat until the first side is browning well; about 4 to 5 minutes. Flip the patties then add the sliced onions around them, nestling them into the drippings that have formed.
Cook on the second side until firm and cooked through. You can reduce the heat to medium low if needed, cook about 5 to 6 minutes more. You can check the internal temp on your patties if you want to. It should be 165.
Make the gravy
Take the patties out of the skillet and transfer them to a plate. Leave 2 tablespoons drippings in the pan with the onions and drain off any excess.
Place the pan over medium low heat and add the flour. Stir until no pockets of dry flour remain; about 1 minute.
Add the beef broth and stir to combine. Cook until the mixture bubbles and thickens; about 2 to 3 minutes. Add salt and extra pepper if desired and a dash or red wine is nice here if you feel the gravy needs a bit of acid, but it's optional.
Transfer the patties back into the gravy and let everything bubble together for a minute. Serve warm.
Notes
Note 1: I use avocado oil but any flavorless oil is fine here. You could even use a bit of melted beef tallow. Note 2: For gluten free, use a 1:1 gluten free flour blend. For arrowroot starch use 2 tablespoons and add to the drippings; proceed with the recipe. Note 3: Pacific Foods and Kettle and Fire make good beef broths if you don't have homemade. Avoid using bouillon cubes or powders.