Preheat the oven to 220C, fan-forced. Line an oven tray with baking paper. Cut the unpeeled sweet potato and unpeeled potato into 1.5cm-thick wedges. Crush or finely chop the garlic. Put the wedges on the lined tray, scatter over the garlic and drizzle with 3 tsp olive oil. Season the wedges with salt and pepper and turn to coat. Roast for 25-30 mins until golden.
Step 2 — Prep ingredients
Meanwhile, thinly slice the onion and tomato.
Step 3 — Make dressings
For the mustard mayonnaise, combine the vegan mayonnaise and 2 tsp dijon mustard in a bowl and season with pepper. For the vinaigrette, put 2 tsp extra virgin olive oil, 1 tsp balsamic vinegar and 1 tsp dijon mustard in a large bowl, season with salt and pepper and whisk to combine.
Step 4 — Cook patties and onion
Heat 2 tsp olive oil in a medium frypan over medium-high heat. Cook plant-based patties for 4-5 mins each side until golden. Remove from the pan. Heat 2 tsp olive oil in pan over medium heat. Cook onion, stirring regularly, for 4-5 mins until softened. Add barbecue seasoning, 1 tsp sugar and 1 tsp balsamic vinegar and cook, stirring, for 30 secs or until caramelised.
Step 5 — Toast bread rolls
While the onion is cooking, halve the bread rolls through the middle. Put the rolls on an oven tray, cut-side up, and bake for 6 mins or until lightly toasted.
Step 6 — Get ready to serve
Divide the shredded vegan cheddar, patties and onion among the roll bases. Bake for 6-7 mins until the vegan cheddar is softened. Spread the roll tops with mustard mayonnaise. Add the tomato to the roll bases, then sandwich with the roll tops. Add the salad leaves to the vinaigrette dressing and toss to coat. Serve the burgers with the wedges and salad.