Add black beans, paprika, garlic powder, cumin, and salt to medium saucepan over medium heat. Stir well to combine, then cook 5 to 6 minutes or until mixture is warm. Taste and adjust seasonings as desired.
Meanwhile, pour 1 cup of liquid from jar of beets into second saucepan and warm over medium-low heat. Once liquid is simmering, add in sliced red onions and cook 3 minutes. Remove pickled onions from heat and set aside.
Add meat of avocados, lime juice, salt, and garlic powder to food processor bowl. Process until mixture is completely smooth.
Assemble tacos by filling each tortilla with sliced beets, warm black beans, pickled red onions, avocado sauce, and any additional toppings you prefer. Serve immediately.
Notes
If your saucepan is too hot, you'll overcook the beans which can make them dry and crumbly. If that happens, just stir in approximately 3 tablespoons of water.