Set your oven to its lowest setting. Soak the skewers in a dish or bowl of water (this will help stop them burning later on). Tumble the chicken into a bowl with 2 tsp Cajun seasoning and 2 tsp olive oil. Mix well and set aside to marinate.
Roughly chop the pepper, discarding the seeds and stem. Pop into a small pan. Peel 1 of the garlic cloves. Slice it. Add it to the pan with 100ml water, 1 tbsp red wine vinegar and a good pinch of salt and pepper. Cover and simmer for 15 mins, or till tender, adding a little more water if needed. Blend till smooth with a hand-held blender or leave chunky. Taste and adjust the seasoning.
Set a large frying pan over a high heat. Thread the chicken onto the skewers. Press into the hot pan using a spatula, or use the weight of a smaller, heavy frying pan. Cook for 7 mins on each side, or till the meat is cooked all the way through – the juices should run clear when pierced with a knife.
Pop the chicken skewers in a dish and keep warm in the oven. Keep the pan on the hob and turn the heat right down. Drain the beans. Tumble them into the pan with a good pinch of salt and pepper. Peel and chop the other garlic clove and the coriander stalks. Add the garlic and stalks to the pan with 1 tbsp red wine vinegar. Cook for 3-4 mins, till the beans jump and crisp up a little.
Pile the black beans onto plates. Roughly chop the coriander leaves and scatter half over the beans. Set the chicken skewers on top.
Halve, stone and peel the avocado. Thinly slice it. Fan the avocado slices next to the black beans. Dust a little salt and pepper over. Pour the pepper sauce into a small dish for dipping, or just drizzle it alongside the beans. Sprinkle over the remaining coriander to serve.