Chilli seared tuna with avocado cream and grilled corn

Ingredients

• 4 chipotle chillies
• 1 tablespoon olive oil
• 1 small brown onion (80g), chopped finely
• 2 cloves garlic, crushed
• 1/3 cup loosely packed fresh oregano leaves
• 2 tablespoons tomato paste
• 2 tablespoons water
• 4 x 200g (6½-ounce) tuna steaks
• 2 trimmed corn cobs (500g)
• 8 x 20cm (8-inch) flour tortillas
• 2 limes, cut into wedges
• 2 small avocados (400g), chopped coarsely
• 1/2 cup (120g) sour cream
• 1/4 cup coarsely chopped fresh coriander (cilantro)
• 1 tablespoon lime juice