Preheat your oven to 400°F (200°C) if baking the taquitos. Line a baking sheet with parchment paper for easy cleanup.
In a mixing bowl, combine the cooked black beans, mashed sweet potatoes, corn, cumin, paprika, garlic powder, and a pinch of salt. Mix well until all ingredients are evenly combined.
If using corn tortillas, warm them in a dry frying pan for about 10-15 seconds on each side, until pliable.
Take a tortilla and place a generous spoonful of the filling mixture on one end. Roll the tortilla tightly, tucking in the sides as you go to seal the taquito.
Place the rolled taquito seam-side down on the baking sheet. Repeat with the remaining tortillas and filling.
If baking, lightly spray the taquitos with olive oil and bake for 20-25 minutes, turning halfway through, until golden and crispy.
If frying, heat oil in a frying pan over medium heat. Place a few taquitos in the oil, frying until golden brown on all sides.
Serve hot with avocado or guacamole and salsa if desired.