Chilli-Seared Tuna with Avocado Cream Tortillas and Grilled Corn

4 chipotle chillies
1 tablespoon olive oil
1 small brown onion, chopped finely
2 cloves garlic, crushed
1/3 cup loosely packed fresh oregano
2 tablespoons tomato paste
2 tablespoons water
4 x 200g tuna steaks
2 trimmed corn cobs
5 large flour tortillas
2 limes, cut into wedges

for the avocado cream
2 small avocados, chopped coarsely
1/2 cup soured cream
1/4 cup coarsely chopped fresh coriander leaves
1 tablespoon lime juice

Place chillies in small heatproof bowl of boiling water; stand 15 minutes. Drain; chop chillies coarsely.

Heat oil in small frying pan; cook onion and garlic, stirring, until onion softens. Stir in chilli, oregano, paste and the water; bring to a boil. Remove from heat; blend or process, pulsing, until mixture forms thick paste.

Place fish, in single layer, in large shallow dish; using fingers, pat chilli paste into both sides of fish. Cover; refrigerate 30 minutes.

Meanwhile, make avocado cream - (Blend or process avocado and soured cream until smooth; stir in coriander and juice.)

Cook corn on heated oiled grill plate (or grill or barbecue) until browned lightly and just tender; slice thickly, cover to keep warm. Cook undrained fish on same heated oiled grill plate until browned both sides and cooked as desired. Cover; stand 5 minutes. Slice fish thickly.

Meanwhile, heat tortillas according to manufacturer's instructions.

Divide fish, corn, avocado cream and tortillas among serving plates. Serve with lime wedges.