Preheat the oven to 220°C/200°C fan/gas mark 7.
Halve the aubergine lengthways and score the flesh in a criss-cross pattern about 1cm deep. Place on a baking tray with a drizzle of vegetable oil and roast for 20–25 minutes, until soft and melty.
Meanwhile, chop the potatoes into 1cm-thick fries and toss on a second baking tray with a drizzle of vegetable oil and a pinch of salt. Roast for 20–25 minutes until golden.
Finely dice the red onion and crush 1 garlic clove. Heat a drizzle of vegetable oil in a deep-sided pan over a medium–high heat. Add the onion and fry for 3–4 minutes until soft, then add the crushed garlic, tomato purée, ancho chilli powder and oregano. Fry for 1–2 minutes more, then drain and rinse the black beans and add to the pan. Crumble in the stock cube and pour over 200ml boiling water. Bring to the boil, then reduce the heat and leave to simmer for 15 minutes.
Once the aubergine is ready, remove from the oven and remove and discard the skin. Pull apart the flesh and add this to the black bean mix. Roughly chop the cherry tomatoes and add to the pan. Stir and leave to simmer while you wait for the fries to finish cooking.
Peel and stone the avocado and peel the remaining garlic clove. Add to a blender with two-thirds of the coriander and 3 tablespoons of water. Squeeze in the lime juice and blend until smooth. Chop the remaining coriander.
Serve the fries covered in the pulled aubergine mix, topped with the avocado sauce. Finish with the remaining coriander.