Slice your potatoes in half and hollow out each 'skin'. Drizzle with olive oil and season. Bake for 20 minutes at 180°C. Heat 1 tbsp olive oil and fry the onion for 1 minute. Add the beef mince and break up into chunks. When nearly completely browned, add garlic powder, salt and pepper. Add worcestershire sauce, mustard and ketchup. Stir to combine. Dollop into burger skins and top with grated cheddar. Bake at 220°C for 10 minutes. Serve with gherkin!