Top and tail your beans then cut each into 3 (size is really up to you)
Put a pot of water on to boil, when water is boiled drop in your beans and blanch for 1 minute.
Drain your beans and plunge into cold water. Drain when cooled and set aside in a bowl.
In a non stick frying pan toast your sesame seeds until just browned. Set aside to cool.
Thinly slice your onion. My preference is to slice from base to tip, not make slices like a 1/4 circle.
Add onion, pepper and 3/4 of your sesame seeds to your beans and give a quick mix.
Add only enough mayo to just thinly coat your beans. If you think the mayo is a bit thick, thin it out with milk first. Mix well.
Sprinkle over the rest of the sesame seeds and add a bit more cracked pepper.