Line a baking sheet with aluminium foil and place a wire rack over it. Line the bacon on the wire rack. Avoid the bacon slices from touching other slices.
Bake in the oven until the bacon sizzles and crisps, about 15 minutes.
Prepare the patties
Form the ground yak into patties. Throw from palm to palm about 10 times to let the air out.
Salt and pepper both sides of the patties.
Sprinkle garlic powder and onion powder on one side of the patties.
Grill
Heat the griddle at medium-high and lightly grease with vegetable oil.
Place the patties on the grill and cook until grill marks are formed.
Slice the brioche buns in half and place them on the grill until grill marks are formed.
Place the onion slices on the grill and cook until grill marks are formed.
Turn the patties over and grill until the meat is cooked, but be careful not to overcook them.
Turn the buns over and grill until grill marks are formed on both sides.
Serve
Serve deconstructed or assembled. To assemble, place the bacon, cheese, patty, tomato, lettuce and onions between the buns. Pierce vertically through the middle with a thin bamboo stick to keep the burger together.