Preparation

• 1
  Whisk the egg yolk with 2 tablespoons of lemon juice, the dijon mustard and a clove of crushed garlic. Gradually add 3-4 tablespoons of olive oil, whisking continually, until the aoli is thick and smooth. Season to taste with salt, cover and chill.
• 2
  Stir together 4 tablespoons of balsamic vinegar and 2 tablespoons of olive oil, seasoned with salt and back pepper. Wipe the mushrooms and then marinade them in the oil and vinegar.
• 3
  To caramelise the onions, peel and finely slice the onions and saute gently in 2 tablespoons of olive oil for 10 minutes, stirring occasionally. Stir in 2 tablespoons of balsamic vinegar and the sugar and continue to cook very gently for 15 minutes.
• 4
  Place the marinated mushrooms upside down under a hot grill for 2-3 minutes, then turn them over. Grill for another 2 minutes then place a slice of cheese on top and grill very briefly to melt it. Meanwhile, split and lightly toast the rolls.
• 5
  Wash the rocket, thinly slice the tomatoes then peel and slice the avocado.
• 6
  Spread aoli on the bottom of each roll then add rocket and sliced tomato. Place a mushroom and cheese on the top and then add a generous spoonful of caremelised red onion and a few slices of avocado before adding the top of the bread roll.