Preheat the oven to 220C, fan-forced. Line an oven tray with baking paper. Cut the unpeeled sweet potatoes into 1cm-thick wedges. Put on the lined tray, drizzle with 2 tsp olive oil, season with salt and pepper and toss to coat. Roast for 20 mins or until golden and tender.
Step 2 — Make slaw
Meanwhile, thinly slice the cabbage with a sharp knife or mandoline. Thinly slice the onion. Put the cabbage and onion in a bowl, add 1 tsp red wine vinegar and season with salt and pepper. Using your hands, massage for 1 min or until slightly softened.
Step 3 — Prep haloumi
HALOUMI OPTION Combine the sriracha (sriracha is a hot chilli sauce; if you prefer less heat, reduce or omit it), ¾ tsp Spanish seasoning and 1 tbs olive oil in a large bowl and season with salt and pepper. Slice the haloumi. Add the haloumi to the marinade and turn to coat.
Step 4 — Cook haloumi
Heat a medium frypan over medium-high heat. Cook the haloumi for 2 mins each side or until golden. Remove from the pan.
Step 5 — Make spiced aioli
Turn the oven to the grill mode and preheat to high. Halve the buns through the middle. Put on an oven tray, cut-side up, and grill for 1-2 mins until lightly toasted. Combine the aioli and ½ tsp Spanish seasoning* in a bowl and season with salt and pepper.
Step 6 — Get ready to serve
Spread the aioli over the buns. Divide the haloumi and slaw in alternating layers among the bases. Sandwich with the bun tops. Serve with the sweet potato wedges.