Preheat the oven to 200°C, fan 180°C, gas 6. Wash the potatoes and cut into finger-width chips. Spread in a single layer on a large non-stick baking tray and drizzle with 1 tablespoon olive oil. Bake for 45 minutes, turning a few times.
Meanwhile, heat the remaining olive oil in a large frying pan and add the onion, garlic and dried mixed herbs. Cook for 5 minutes until soft, then tip into a large bowl and add the beef mince. Season and bring the mixture together with your hands. Divide into 4 and shape into burgers.
Using the same pan you used to cook the onion mixture, fry the burgers for about 3 minutes on each side. Transfer to a baking sheet and cook in the oven for a further 10 minutes, until cooked through, piping hot and no pink colour remains.
Serve each burger in a giant white bap with 2 slices of tomato and some salad.