Sweet potato tacos

Name: Sweet potato tacos
Ingredients: 1 red onion, sliced; 3 limes, juiced; 4 sweet potatoes, peeled and cubed; 2 tbsp olive oil; 2 tsp hot smoked paprika; 1 tsp ground cumin; 1 tsp ground coriander; 400g can of black beans, drained and rinsed; 2 ripe avocados, mashed; 2 large ripe tomatoes, deseeded and cubed; 8 small flour tortillas; 50g feta, crumbled (optional); soured cream and torn coriander to serve (optional)