Barbecued prawns and heirloom tomato salad

Ingredients

• 2 cloves garlic, chopped
• 1 hot green chilli, chopped
• 1 cup flat-leaf parsley florets
• 1 cup coriander leaves
• 2 tablespoons red wine vinegar
• 1/2 teaspoon salt
• 1/4 teaspoon ground cumin
• 90 millilitres extra-virgin olive oil
• 16 large australian prawns, thawed if frozen
• olive oil
• 6 heirloom, or homegrown tomatoes, sliced
• 1 avocado, halved, stoned, skinned and sliced
• half small red onion, thinly sliced
• sea salt