To make the dressing, put the pesto, mayonnaise and lemon juice in a large bowl, season with salt and pepper and mix to combine. Add the chicken and stir again. If possible, leave it to marinate for several hours or overnight.
Place the avocado slices in a separate bowl, pour over the lemon juice and toss so the avocado is completely coated.
Cut the cucumber in half lengthways, use a teaspoon to remove and discard the seeds and then peel using a potato peeler. Cut into crescent-shaped slices and arrange these in layers with the avocado slices, tomato halves and pesto chicken. Season with salt and pepper. (If assembling ahead, do not add salt until just before serving.)
Scatter over the toasted pine nuts, micro salad and basil leaves to finish.