In a large bowl mix together the mushrooms and beef – it’s easiest to do with your hands.
Heat the oil in a deep frying pan and add the onion. Fry over a gently heat for 2 to 3 minutes until just soft. Add the mushroom mix and keep cooking for another 5 minutes until the meat is browned all over and the mixture is dry.
Add the green pepper, garlic and paprika. Stir thoroughly. Cook for a further minute.
Add the Worcestershire sauce, puree and sugar and 2 tbsp of water. Stir again and leave to simmer for about 5 minutes until the liquid has evaporated. Season with salt and pepper.
Half slice open the baguettes and spoon the mixture. Top with the gherkins and cheese.