Slice the baby buttons into quarters and place in a large mixing bowl.
Quarter the cherry tomatoes and add them to the bowl. Brunoise or finely dice the red pepper and add it to the mix.
Finely slice the basil and add it to the bowl along with the olive oil, basil pesto, vinegar, fresh chilli and a good amount of salt and pepper. Toss everything until well coated.
Slice the avos in half and carefully peel them and remove the pips. Cut a small piece off the bottom of each half so that they can sit flat on a plate.
Brush the avo halves generously all over with lemon juice.
Spoon the mushroom mixture into each half and serve with an extra wedge of lemon.