For the beef filling, fry the mince in a frying pan over a medium-high heat for 5-6 minutes, stirring occasionally and breaking it up with a wooden spoon, or until browned. Add the onion, mushrooms if using, green pepper and garlic and cook, stirring occasionally, for five minutes or until the vegetables are softened. Stir in the paprika and cumin and season to taste with salt and freshly ground black pepper. Pour in the beef stock and tomato purée and mix well. Cover and simmer gently for 10-15 minutes, stirring occasionally. Meanwhile, for the guacamole, place all the ingredients into a food processor and pulse with to a fine paste. If necessary, loosen the consistency with a splash of water. To serve, place the taco shells on a baking tray and warm them in the oven for 2-3 minutes. Place a leaf of lettuce into the base of each taco shell and spoon on some beef filling into the warm taco shells. Top with a tablespoon of the guacamole and a little sour cream. Finally, garnish with the sliced spring onions.

Suggested acompanying wine: DELICATA Medina Sangiovese I.G.T. Maltese Islands