Preheat the oven to 220C, fan-forced. Bring a medium saucepan of water to the boil for the vegetables. Thinly slice the capsicum. Crush or finely chop the garlic. Cut the cauliflower stem into 1cm chunks, then cut the head into small florets. Thickly slice the carrot and celery. Halve the olives.
Step 2 — Marinate beef
Combine the garlic, 2 tsp Italian seasoning and 2 tsp olive oil in a large bowl and season with salt and pepper. Separate the beef stir-fry into the marinade, add the capsicum and stir to coat.
Step 3 — Make giardiniera
Cook cauliflower, carrot and celery in the pan of boiling water for 4 mins or until just tender. Drain well. Combine a pinch chilli flakes* (see cooking tip), remaining Italian seasoning, 2 tbs red wine vinegar, 2 tsp olive oil and 1 tsp sugar in a large bowl. Add the cooked vegetables and olives and stir to coat. Taste, then season with salt and pepper.
Step 4 — Toast rolls
Halve the rolls through the middle, taking care not to cut all the way through. Put on an oven tray and bake for 5 mins or until lightly toasted.
Step 5 — Cook beef mixture
Meanwhile, heat a large frypan over high heat until very hot (beef stir-fry is best with hot, fast cooking; get the pan very hot before adding the beef and stick to the short cooking time). Stir-fry the beef mixture for 1-2 mins until the beef is browned and capsicum is tender. Remove from the pan.
Step 6 — Fill rolls and serve
Put the salad leaves in a large bowl, drizzle with 2 tsp of giardiniera liquid and toss to coat. Spread the rolls with pesto, then fill with the beef mixture and some of the giardiniera. Serve the rolls with the salad and remaining giardiniera.