In a large bowl, mix the ground bison with the diced onions, garlic, and parsley until combined.
Add in the onion powder, garlic powder, salt, ketchup, Worcestershire, and pepper, and mix well to combine.
Divide the meat into 4 evenly portioned round patties and set aside.
Heat 1-2 tablespoons of olive oil over medium-high heat in a large pan and add the sliced onions. Cook for one minute, then season with salt.
Cook and continuously stir the onions until they're dark brown and caramelized about 30-40 minutes. Turn off the heat and set aside.
Heat a large skillet over medium-high heat and drizzle in the remaining olive oil. Place the burger patties in the pan. Cook for 2-3 minutes on each side for medium-rare.
Top the burgers with a slice of cheese and let melt for 1-2 minutes.
To assemble, spread some mayo on the bottom of a toasted brioche bun. Put the burger on the mayo, and top it with caramelized onions, crispy cooked bacon, and fresh greens.