Combine all the ingredients for the meat mixture and lightly mix with fingertips until just combined. Divide the beef into four 4-ounce patties.
In a skillet medium-high heat, add 1 tablespoon of oil and brown the patties until the are browned on both sides. Remove the patties from the pan and place into the bottom of the crock pot.
Into the same skillet, add the sliced onions and mushrooms, reducing the heat to medium. Cook for 3 to 5 minutes, or until the onions begin to soften. Next, deglaze the pan by adding the beef stock.
Meanwhile, in a small bowl combine cornstarch and 1/4 cup of water. Mix well to form the slurry and set aside.
Once the beef broth mix comes back up to a simmer, add the cornstarch slurry and stir well. Once the gravy comes to a full boil it will start to thicken. Pour the thickened sauce over the patties.
Cover and cook on low for 3 hours.
Suggest serving with mashed potatoes and peas. Garnish with a sprinkling of parsley and chives.