Zest the lime into a bowl. Slice off the skin and pith with a sharp knife. Squeeze any juice from the skin into the lime zest bowl. Chop the lime into chunky segments. Set aside.
Heat a frying pan over a medium heat. Toss in the coriander seeds and toast for 1-2 mins till fragrant. Tip into a bowl and set aside.
Turn the heat down low. Pour 1 tbsp oil into the pan. Add the lime segments. Fry for 30 seconds-1 min till lightly caramelised. Tip into the lime zest bowl, along with any pan juices. Stir in a pinch of salt and pepper.
Peel, stone and roughly chop the avocado. Peel and thinly slice the onion. Halve the tomatoes. Trim the leaves off the radishes (see our tip about the leaves). Quarter or halve the radishes. Combine all of the vegetables in a large mixing bowl.
Tear the coriander leaves into the salad. Add the toasted coriander seeds, caramelised lime segments and their juices. Toss to mix. Pile the salad onto plates and serve.