Put the sweet potato cubes on a baking tray with half of the oil and half of the Mexican seasoning. Stir so all the potato is coated and bake at 200°C/400°F/Gas 6 for 30 minutes.
Heat the rest of the oil in a frying pan and sauté the onions and garlic for 2-3 minutes, or until softened.
Add the black beans, sweetcorn and remaining Mexican seasoning. Mix well and cook for 3-4 minutes. Add the juice of a lime.
Add the cooked sweet potato and heat through.
Assemble the tacos by adding some of the bean/potato mixture, then top with chopped spring onion (scallions), cubed avocado, crumbled feta and chopped coriander (cilantro).
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Notes
Add some extra sweetness by drizzling some honey over the tacos before serving.
You could add some extra crunch to these tacos by sprinkling over some pine nuts or sunflower seeds before serving.
Why not try something different and swap the sweet potato for butternut squash.
Make extra of the roasted sweet potatoes, are they are great to have in the fridge to add to salads for lunch.