Pickled Onion and Cucumber Salad | Australian Onions

Ingredients

• 3 medium white onions (500g), peeled
• 6 large Lebanese cucumbers (1kg), washed
• 1 tbsp fine table salt
• 1 tsp mustard seeds
• 1 ⅓ cups water
• ⅔ cup apple cider or white vinegar
• 1 ½ tbsp caster sugar
• 1 tsp coarsely ground black pepper
• Small mint leaves, to serve