Rinse and dice tomatoes. Rinse the lettuce, shake dry and cut into small pieces. Halve the avocado, remove the stone and peel the avocado halves. Cut the avocado meat into small cubes and drizzle with lemon juice.
Dressing:
Rinse the chilli pepper, cut in half lengthways, remove the seeds and chop the pod. Peel the onion or shallot and dice finely. Mix the chopped chilli, diced shallots, oil, vinegar, sherry and mustard together. Season with salt and pepper and pour over the prepared salad ingredients. Rinse the chives, shake dry and cut into fine rolls. Sprinkle over the salad.