Heat a large skillet over medium-high heat. Then add one tablespoon olive oil and the garlic. Cook until the garlic is fragrant, about 15 seconds.
Add the onion and cook until very soft and caramelized, about 10 minutes.
Add the bison meat and sprinkle with the salt. Cook until no longer pink.
Add the remaining tablespoon of olive oil, chili powder, and chipotle powder, and cook for 2 minutes.
Add the water and tomato paste, stirring to combine and cook until the meat is coated and the liquid has evaporated, about 3–5 minutes.
To make the sauce, combine all of the sauce ingredients in a small bowl and whisk to combine.
Serve the tacos on soft corn tortillas with diced white onion, fresh cilantro leaves, sliced avocado, and the chipotle sauce.