Place the turkey tenderloin and the rest of the ingredients from the list in a deep pot, cover and cook for 30 minutes over medium heat. When the turkey's ready, shred it and place it in a bowl. Preparing the pickled onions is very easy: Add the sliced purple onions to a small pot and boil in two cups of water for 5-7 minutes. Turn off the stove, throw out the water and add the vinegar, pickling spice and salt to the hot onions. Give the onions several minutes to turn pink at room temperature, and refrigerate until you’re ready to put the salbutes together. Grind a cup of cooked black beans and some of the bean broth in a blender until you have a thick sauce. To prepare the salbutes, place the tostadas on a serving dish and add a tablespoon of the thick bean sauce to each tostada, then the shredded turkey and grated cabbage. Lastly, add some pickled onions and garnish with edible carnations.