Lightly toast the walnuts for a couple of minutes and set aside.
Chop the coriander leaves and put them in mortar together with the oils and chipotle paste.
Deseed and chop the chilli then add to the mortar. Add the cumin and grind with the pestle until you get a tough paste. Add the lime juice and salt and pepper. Taste, adjust the lime juice and seasoning. Set aside.
Scatter the salad leaves onto a platter. Add the onion, tomatoes and coriander leaves. Toss well.
Cut the avocado in half, remove the stone, then the skin and cut the flesh into chunks. Add these to the salad. Crumble the walnuts on top.