Soften the onion, garlic, and ginger in the olive oil over a medium heat.
Once cooked, cool.
Really finely chop or better still mince the prawn flesh, the finer the better, and then place into a bowl.
Add the egg white, mayonnaise, juice and zest of lemon and season well with the chilli, pepper and salt.
Mould into 8 small balls then flatten slightly. Press in the sesame and black onion seeds.
Heat the butter and oil in a frying pan and gently sauté the burgers for a minute or two on each side, do not overcook.
Serve in small burger buns or baps.
Make the sauce by peeling and chopping the avocado flesh into 1⁄2 cm pieces, place into a bowl.
Crush slightly with a fork, then mix in the yogourt, garlic, vinegar and salt and pepper, mix well.
Serve on the burger.