1½ tbspbrown mustard seeds1/3 cupwhite wine vinegar1/3 cupdry white wine1 tbspcaster sugar1small red onion, thinly sliced4 Lebanese cucumbers, peeled into ribbons2 tbsplemon juice1/3 cupextra-virgin olive oil2 punnets baby cucumbers, quartered lengthways2 (250gm each) white cucumbers, peeled, seeded, thinly sliced lengthways3 cupsfirmly packed watercress sprigs2/3 cupfirmly packed mint leaves
Combine mustard seeds, vinegar, wine, sugar and 1/3 cup water in a saucepan, season to taste, then bring to the boil over medium-high heat. Add red onion and simmer for 2 minutes, remove from heat, then add Lebanese cucumber and stir to combine. Stand for 5 minutes, then using a slotted spoon transfer cucumber and onion to a bowl. Return pan to heat and simmer for 5 minutes or until reduced to 1/3 cup, remove from heat and whisk in lemon juice and olive oil and season to taste. Cool.
Combine pickled cucumber and red onion, baby and white cucumbers, watercress and mint in a large bowl with mustard seed dressing and toss to combine. Arrange in a bowl and serve immediately.