Preheat the oven to 425 Degrees F. Line a shallow-sided baking pan with parchment paper. Combine the first 7 ingredients in a bowl. Moisten your hands with cold water, shape meat into four, 3/4" thick oval patties, and set on the baking pan. Roast the hamburger steaks 10 minutes. Turn over and roast 10 minutes more, or until richly coloured and cooked through.
While hamburger steaks cook, heat oil in small pot set over medium heat. And the onion and cook until tender, about 5 minutes. Stir in the flour and cook and stir 2 to 3 minutes more. Slowly, while stirring steadily, mix in the stock. Bring to a simmer and simmer until thickened gravy forms. Season with salt and pepper, cover and reserve on low heat until the steaks are ready.
When ready, plate the hamburger steaks, top with gravy and serve.