Heat oven to 350 degrees Fahrenheit. In a baking dish, toss onions, mushrooms, and oil together and place in the oven. Roast for 30 minutes. Add Balsamic vinegar to onion and mushroom mixture, stir, and roast for another 10-15 minutes, or until onions are caramelized to your liking.

While the onions and mushrooms are roasting, combine the ingredients for the burgers and form into 4 patties.

Heat oil a cast iron or other heavy-bottomed skillet over medium heat. When oil is hot, add the patties to the skillet. Cook the patties, turning several times, until they are cooked through and internal temperature reaches 165 degrees Fahrenheit. If the skillet gets too hot, turn it down as necessary to preventil the burgers from burning. You want them to be a nice, golden brown, not charred.

Assemble the burgers by topping each burger with a slice of cheese, a slice of cooked bacon, 2 tablespoons of BBQ Sauce and 1/4 of the caramelized onions and mushroom mixture. As an optional step, you can add a tablespoon of mayo, lettuce, and/or tomato to the bottom half of the bun.