Preheat the oven to 200C, fan-forced. Line an oven tray with baking paper. Thickly slice the onion into rounds and put on the lined tray. Drizzle with 1 tsp olive oil and toss to combine (the onion will separate into rings). Season with salt and pepper. Roast for 15 mins or until tender. Cover to keep warm.
Step 2 — Prep slaw ingredients
Meanwhile, shred the cabbage with a sharp knife or mandoline. Thinly slice the cucumber and chives.
Step 3 — Prep patties
Put the pork mince, breadcrumbs, half the barbecue sauce and 1 egg in a large bowl and season with salt and pepper. Using damp hands, combine well, then shape into 2 equal patties, slightly larger than the base of a bun.
Step 4 — Cook patties
Heat 2 tsp olive oil in a medium frypan over medium-high heat. Cook the patties for 3 mins each side or until cooked through. Spread the patties with the remaining barbecue sauce. Remove from the pan and rest for at least 3 mins.
Step 5 — Toast buns
While the patties are cooking, halve the buns through the middle. Put on an oven tray, cut-side up, and bake for 6 mins or until golden.
Step 6 — Toss slaw and serve
Whisk 2 tsp extra virgin olive oil and 1 tsp red wine vinegar in a large bowl until combined. Season with salt and pepper. Add the cabbage, cucumber and chives and toss to combine. Spread the buns with the burger sauce. Layer the bases with some of the slaw, the pork patties and onion, then sandwich with the bun tops. Serve with the remaining slaw.