Steam the courgette (zuchini) slices over boiling, salted water for about 3 minutes until tender; cool completely. Cut avocado in half length ways, discard stone and scoop flesh into a blender or food processor.
Add courgettes and process until smooth. Transfer to a medium bowl. Stir in onion, chilli powder, oil and vinegar.
Mix well and season with salt. place a tablespoon of the mixture on each slice of beef, roll up and secure with a cocktail stick; reserve any remaining avocado mixture.
Place lettuce leaves on a flat serving plate. Arrange the beef rolls in a circle, like the spokes of a wheel. Scoop out and sieve egg yolks.
Place in the centre of the serving dish. Cut egg whites into thin strips and place on the roast beef rolls.
Garnish with radishes. Serve any reserved avocado mixture separately.