Bring the white wine vinegar, sugar, garlic, spices, peppercorns, bay leaf and onion to the boil in a large non-reactive pan. Reduce the heat to a simmer and simmer the mixture for 4-5 minutes.
Remove the pan from the heat, then add the salmon fillets and courgette batons and stir to coat them in the marinade mixture. Set aside until completely cooled. Cover the pan and chill in the fridge for 1½-2 hours.
When the pickled salmon has chilled and marinated, mix together the broad beans, butter beans and cherry tomato halves in a bowl. Pour over a little of the chilled marinade liquid, to taste, and stir well to combine.
To serve, divide the dressed beans and tomato mixture equally among six serving plates. Place one pickled salmon fillet on top of each. Spoon over some of the marinated onion, garlic and courgette pieces. Drizzle some of the remaining marinade liquid around the edge of each plate. Sprinkle over the mustard cress.