Preheat the oven to 220°C (425°F) (200°C/400°F fan-forced).
Place the potatoes in a large baking dish so that they are evenly spread out (use two baking dishes, if required, to ensure the potatoes are not overlapping). Sprinkle the potatoes with salt and pepper and drizzle with olive oil. Toss to coat.
Bake for 40 minutes or until crisp and golden, turning once halfway through.
Heat the olive oil in a large, deep, heavy-based frying pan over medium–high heat. Add the onion and cook, stirring, for 1–2 minutes until softened.
Add the beef and cook for 4–5 minutes or until it’s starting to brown, breaking up the beef as you go.
Add the remaining beef ingredients and cook for a further minute. Set aside.
Combine the burger sauce ingredients, except the water, in a medium bowl. Add 1 tablespoon of water at a time until your desired consistency is reached.
Divide the lettuce among four bowls. Top with the baked potatoes, beef and shredded cheese, followed by the cherry tomatoes, red onion and gherkin. Drizzle with the burger sauce and serve.
