Step 1 Preheat oven to 180°C. Place a non-stick frying pan over medium heat and spray lightly with oil. Add onion and cook, stirring, for 10–15 minutes, or until softened. Set aside.
Step 2 Thoroughly combine breadcrumbs, carrot, zucchini, mince, barbecue sauce, cumin and mint in a large bowl. Divide mixture into 4, then form into patties.
Step 3 Place a large non-stick frying pan over medium heat. Spray meat patties with oil. Cook patties for 3 minutes on each side, or until golden brown. Transfer to a foil-lined tray and place into oven. Cook for 10 minutes, or until cooked through. Add bread rolls in last 3–5 minutes of cooking, to lightly toast.
Step 4 Meanwhile, cook haloumi slices for 2 minutes each side, or until golden and crispy.
Step 5 Place the bases of the bread rolls onto 4 serving plates. Spread each bottom half with 1 tablespoon tzatziki, then top with baby spinach, lamb patties, capsicum strips, haloumi and onion. Finish with the top of rolls to serve.