Drain the black beans and rinse them with cold water. Shake dry and tip them into a large bowl.
Slice the cherry tomatoes in half. Halve the chilli, flicking out the seeds and white pith if you prefer less heat, and finely chop it. Peel the red onion and finely slice it. Add the tomatoes, chilli and onion to the bowl.
Finely grate in the lime zest and squeeze in the juice. Pour in 1 tbsp olive oil and season with salt and pepper.
Halve the avocado and scoop out the stone. Scoop the flesh out of the skin and slice it. Add the avocado slices to the bowl, along with the rocket.
Toss everything together, then pile the salad onto a couple of plates. Crumble over the feta to serve.