Divide ground bison into four portions and gently form each portion into four individual round patties. Make a deep indentation in the middle of each patty.
Arrange bacon strips on a baking sheet and cook in oven until crisp. Drain on a paper towel and set aside.
Meanwhile, heat oil in a skillet over low heat. Cook sliced onions until caramelized. Remove from heat and set aside. Add additional oil to skillet, as needed. Saute mushrooms until tender, around 1 to 2 minutes. Pour in steak sauce and simmer for an additional 1 minute. Keep mushroom sauce warm.
Warm hamburger buns.
In a skillet, heat oil. Pan-fry burger patties to desired doneness, turning once. Preferably, for food safety, cook burger to a minimum of 160 F.
Layer lower part of hamburger buns with pepper jack cheese, crisp bacon, and beef patties. Spoon mushroom-steak sauce on patties. Top with caramelize onions and upper part of buns.
1) The deep indentation on center will help burger cook evenly and will keep patties from “plumping” up.
2) Handle and shape burgers lightly. Too much pressure will toughen meat and will result to a dense, heavy burger.
3) Use tongs or spatula to turn and flip burgers. Forks will pierce burgers which will allow precious juices to escape. For the same reason, do not flatten or press on patties.