Remove crusts from bread slices, toast and halve each slice. Cut avocado in half, remove seeds, remove the peel and cut flesh into thin slices. Sprinkle with lemon juice. Blanch tomato in boiling water, peel, remove seeds and cut flesh into cubes.
If desired, spread toast with butter. Lay avocado slices on toast in a fan arrangement, sprinkle with sesame seeds and chives and garnish with some tomatoes. Place on a serving dish and serve.