Preheat the oven to 200C, fan-forced. Line an oven tray with baking paper. Cut the unpeeled potatoes into 1.5cm-thick chips.
Step 2 — Roast chips
Put the potato on the lined tray, drizzle with 1 tsp olive oil, scatter over half the barbecue seasoning and toss to coat. Roast the chips for 20-25 mins until golden and tender.
Step 3 — Cook patties
While the chips are roasting, heat 2 tsp olive oil in a medium frypan over medium-high heat. Cook the plant-based patties for 4-5 mins each side until golden.
Step 4 — Toast rolls
Meanwhile, halve the rolls through the middle. Put the rolls on an oven tray, cut-side up, and bake for 5 mins or until lightly toasted.
Step 5 — Make zesty guacamole
While the rolls are baking, thinly slice the spring onion. Finely grate the lemon zest, then juice half the lemon*. Put the guacamole in a bowl. Add the spring onion, lemon zest and 2 tsp lemon juice and stir to combine.
Step 6 — Get ready to serve
Thinly slice the tomato. Combine the mayonnaise and remaining barbecue seasoning in a bowl. Spread the cut sides of the rolls with the mayonnaise mixture. Divide the patties, tomato and guacamole among the roll bases, then sandwich with the roll tops. Serve with the chips.