In a medium mixing bowl, mash the black beans with the implement of destruction of your choice - fork, potato masher, pastry cutter, etc. Alternately, you could give it a couple of pulses in a food processor or a blender, but don't go overboard, you want the beans to be chunky, not a paste.
In a large skillet, begin to brown your bison. Break apart the meat as you go, but leave it crumbly. Cook to medium done-ness, and add the beans. Combine the meat and beans until evenly mixed.
Continue to cook your bison and beans until the meat is well browned (5-6 minutes). Add in the garlic, sesame oil, ketchup, hoisin, soy sauce, rice wine vinegar and sriracha and stir together well. You should have a mixture that's about the texture of oatmeal - wet, but it will hold it's shape on the bun for the most part. If your mixture is too firm, you can add a water, a little bit at a time, until the sloppy joe's are sloppy enough for your taste.
Modified from the Korean Beef Sloppy Joe recipe at Dinner Then Dessert.