Peel the sweet potatoes and cut them into fairly small cubes or into 1cm strips, then put them in a roasting tray.
Coat them in paprika and a small amount of oil until they look roughly covered. Add a sprinkle of chilli powder and/or cayenne pepper if desired, and a touch of salt to your taste.
Put them in the oven and bake until they are cooked and turning golden on top, 30 to 40 minutes.
In the last 10 minutes of the sweet potatoes cooking, fry the spring onions in a small amount of oil until just soft. Put the entire tin of black beans (with liquid) in the pan with the spring onions and cumin to taste, and a sprinkle of salt and pepper. When cooked and liquid is almost entirely evaporated, roughly mash with the back of a fork or wooden spoon. The beans do not need to be entirely smooth.
For the salsa
Dice the jalapeño and red onion as finely as possible. Cube the tomatoes. Put them in a bowl with olive oil, a pinch of salt, coriander and the juice of 1 lime.
Serve the filling in the tacos with salsa.
May also be served with guacamole or simply diced/mashed avocado to soften the spice.