In skillet, sauté mushrooms and onion in butter for 4 minutes. Set aside.
Form ground beef into 4 even patties and season to taste with pepper and steak spice. Grill over medium-high heat for 4 minutes on each side. Just 3 minutes before burgers are done, top each one with 2 slices of Canadian Brie cheese. Heat buns on top shelf. Close lid and continue cooking.
Place burgers in warm buns and garnish with sautéed mushrooms and onion. Serve with chips.