Watermelon, prawn and avocado salad

Ingredients

• 1 small red onion, finely chopped
• 1 fat garlic clove, crushed
• 1 small red chilli, finely chopped
• juice 1 lime
• 1 tbsp rice or white wine vinegar
• 1 tsp caster sugar
• watermelon wedge, deseeded and diced
• 1 avocado, diced
• small bunch coriander leaves, chopped
• 200g cooked tiger prawns, defrosted if frozen