MAKE THE MARINADE: Whisk the balsamic, olive oil, oregano, soy sauce and garlic in a small bowl. Dip the smooth side of each mushroom in the marinade, rubbing to cover evenly, then place mushrooms gill side up in a flat dish and pour over the marinade. Set aside.

COOK THE POTATO WEDGES: Heat the oven to 200°C / 400°F / Gas 6 and line an oven tray with baking parchment paper. Cut the potatoes into thick wedges and transfer them to the prepared tray. Drizzle over the oil and toss well to combine. Sprinkle over the oregano and paprika, then roast in the oven for 30-40 minutes until golden and tender. Season generously with salt and pepper, and keep warm.

PREPARE FILLINGS: While the potatoes are cooking, prepare your ingredients, slicing vegetables, buns, cheese etc. and stirring together the mayonnaise and harissa to make the spicy sauce.

COOK THE BURGERS: When the wedges have been in the oven for 20-25 minutes, cook the portobello burgers. First, heat a little oil in a large skillet or non-stick pan over medium-high heat, then cook the mushrooms for 4-5 minutes on each side until deeply golden brown. Use a pastry brush to brush with the leftover marinade as you go. Next, heat the oven grill/broiler to high.

ASSEMBLE: When your mushrooms are cooked and a rich, deep brown, lay a slice of Swiss cheese on top of each and place under the hot grill until the cheese has melted. Transfer the burgers briefly to a plate lined with a paper towel and gently press them down to drain some excess juices. Finally, assemble your mushroom burgers, topping them with tomato slices and your favourite condiments. Serve hot with the wedges and spicy sauce.