Add the rinsed black beans to a large bowl with a dash of oil and the spices. Toss well to coat, then spread them out in a single layer on a baking tray. Roast at 190°C (Gas Mark 5 / 375°F) for around 25-30 minutes, tossing halfway, until crispy but not overly hard.
To make the dressing, add the fresh coriander (cilantro) to a mini food processor, along with the garlic. Blitz well until finely chopped. Add the lime juice and half an avocado, and blitz again until smooth. Season to taste.
To assemble the taco salad, fill two large bowls with salad leaves, then top with the tomatoes, sweetcorn, chopped spring onions, and 1/2 an avocado. Finish with the roasted black beans and the avocado lime dressing, and serve immediately.