Preheat the oven to 220C, fan-forced. Line 2 oven trays with baking paper. Cut the unpeeled sweet potatoes into 2cm-thick wedges. Put the wedges on a lined tray, drizzle with 2 tsp olive oil and season with salt and pepper, then turn to coat. Bake for 25-30 mins until golden and tender.
Step 2 — Roast capsicum
Meanwhile, cut 4 'cheeks' from the capsicum, discarding the seeds. Put the capsicum on the remaining lined tray, skin-side up, and drizzle with 1 tsp olive oil. Roast for 20 mins or until the skin is slightly blackened. Cover and stand for 5 mins to allow the skin to steam and loosen. Put the capsicum on a board and reserve the tray. Remove the capsicum skin, then cut into strips.
Step 3 — Marinate fish
While the vegetables are baking, put half the fennel seeds* and a pinch of salt in a mortar and pestle (see cooking tip) and grind to a powder. Combine the fennel powder, cumin and coriander spice blend and 2 tsp olive oil in a large bowl and season with salt and pepper. Add the fish and turn to coat.
Step 4 — Cook fish
Heat 2 tsp olive oil in 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 5 — Toast bread rolls
While the fish is cooking, halve the bread rolls through the middle. Put on the reserved tray, cut-side up, and bake for 4-6 mins until lightly toasted.
Step 6 — Make salad and serve
Combine 1 tsp red wine vinegar and 1 tsp extra virgin olive oil in a large bowl and season with salt and pepper. Add the capsicum and rocket and toss to coat. Spread the rolls with the aioli, then fill with the fish and some of the salad. Serve the sandwiches with the wedges and remaining salad.