Brush the 1 tablespoon oil over the tortilla, then cut into thin strips about 5 cm (2 inches) long. Cook under a preheated hot grill for 1 minute on each side, or until crisp and lightly browned. Leave to cool.
Meanwhile, make the dressing by mixing together the lime rind and juice, coriander, chilli powder and ground cumin in a bowl. Slowly drizzle in the oil, stirring all the time. Season well.
When ready to serve, stone, peel and slice the avocados, then arrange on serving plates with the salad leaves and tomatoes. Drizzle over the dressing and serve scattered with the toasted tortilla slices.