Preheat a large skillet over medium heat. Add the olive oil, diced onion, and bison to the skillet and it cook undisturbed for 2-3 minutes to brown the bottom. Continue cooking for another 2-3 minutes, stirring to break up the meat a little (leave it in ½-1 inch chunks instead of tiny crumbles).
Add the dry seasonings (cumin through pepper, or pre-mixed taco seasoning) and tomato paste. Stir well to season the meat, and cook for another 5 minutes, or until the bison is fully cooked and is a deep red-brown color. Remove from heat.
While the bison is cooking, add all the ingredients for the sauce to a small food processor and process until mostly smooth.It will take a few minutes to break down the cilantro. Taste and add more salt, lime juice, or jalapeño to taste. Add water as needed if you want a thinner sauce that can be poured.
Toast the tortillas in a hot skillet and keep them wrapped up in a clean kitchen towel until ready to serve.
Serve by spooning generous amount of bison taco meat onto each tortilla, drizzling with avocado sauce, and adding your favorite toppings, such as diced onion, crumbled cotija cheese, fresh or pickled jalapeños, fresh cilantro.
Notes
If the bison meat seems a little dry, add a splash of water or beef broth (or chicken broth). But usually, meat lets out liquid as it cooks, and since I am using lean bison meat I don't need to drain it. I just add tomato paste and this makes the perfect slightly-sauce consistency for the taco meat.Instead of all the dry seasonings, you can use 2 tablespoons of taco seasoning.You can switch up the ingredients for the sauce based on what you have: mayo, sour cream, and yogurt can all be substituted for each other (more yogurt = tangier sauce, need to add more salt. More mayo = richer sauce, reduce the salt). Cotija can be substituted with feta or skipped. As long as you have some tang from the lime juice, some creaminess, and salt, the sauce will turn out delicious!Nutrition facts are estimated. Actual calories and nutrition will depend on what tortillas you use and how much bison and sauce you add to each taco.