Step 1 Put capsicum, chilli and lemon juice in a food processor; blend to combine sauce and set aside.
Step 2 Bring a medium saucepan of water to the boil. Add pumpkin and cook for 3–4 minutes, or until just tender. Drain pumpkin; leave to steam-dry for 3–4 minutes.
Step 3 Put cooked pumpkin in a large bowl with chickpeas; mash to form a slightly chunky mixture. Add zucchini, cumin, coriander, egg, flour, breadcrumbs and halloumi to pumpkin–chickpea bowl. Stir mixture to combine.
Step 4 Place a large non-stick frying pan over medium–high heat. Add canola oil and heat. Wet hands to shape vegetable mixture into 4 large patties. (See tips for an alternative.) Add patties to pan and cook, turning carefully with a spatula, for 1–2 minutes per side, or until golden brown.
Step 5 Divide baby spinach among sourdough rolls (or wholegrain wraps). Transfer burger patties to rolls, top with reserved capsicum sauce and pickles, and serve.