Mix the melon, strawberries, mango, spring onions and basil well together in a bowl.I used watermelon, cantaloupe and honeydew melon, - but use the ones you prefer or can get hold of. 2 kinds is also plenty.
Drizzle with a tablespoon of the oil and the juice of a single lime, and season with freshly ground pepper.
Tip the melon salad into a serving bowl, top with the avocado cubes, - then taste and decide whether you want more lime juice over it. Whether you need 1 or 2 depends entirely on how juicy your limes are.
Drizzle the remaining oil over the top of the salad, and scatter the finely grated lime zest over the top.
Serve the salad with a little extra freshly ground pepper on top, and if you like, a bowl of crumbled feta or toasted pine nuts on the side, or sprinkled over the salad.