Discard the husk and silks from the corn, then halve. Put the corn and 125ml (½ cup) water in a small saucepan over high heat. Cover and bring to the boil. Reduce the heat to medium and cook for 8-10 mins until tender. Drain. Return to the pan, add 10g butter, season with salt and pepper and turn to coat.
Step 2 — Prep vegetables
Meanwhile, peel the cucumber and carrot into ribbons with a vegetable peeler. Thinly slice the spring onion.
Step 3 — Cook fish
Combine the South American seasoning and a drizzle of olive oil in a bowl and season with salt and pepper. Add the fish and turn to coat. Heat a medium frypan over medium heat. Cook the fish for 3½-4 mins each side until browned and cooked through. Remove from the pan.
Step 4 — Dress salad
While the fish is cooking, whisk 2 tsp extra virgin olive oil and 1 tsp white wine vinegar in a large bowl until combined and season with salt and pepper. Add the cucumber, carrot and spring onion and toss to coat.
Step 5 — Microwave bread rolls
Halve the bread rolls through the middle. Put on a microwave-safe plate, cut-side up, and microwave for 30 secs or until heated through. (If you prefer, you can grill the bread rolls. Put the bread rolls on an oven tray, cut-side up, and grill for 3-4 mins until lightly toasted.)
Step 6 — Assemble rolls and serve
Spread the bread rolls with the aioli. Divide the fish and some of the salad among the bases, then sandwich with the roll tops. Serve with the corn and remaining salad.