Preheat the oven to 180c
While you are waiting for the oven to warm up, cut the avocado in half, remove the stone, scoop out the flesh and place in a small bowl. Lightly mash with a fork, then add the lemon juice and extra virgin olive oil, season then set aside.
Place the sourdough slices on a large baking tray, drizzle over the olive oil, then put in the oven for 8 to 10 minutes, or until crispy and toasted, remove from the oven and leave to cool for 5 minutes.
Once cooled break each piece of toast into 4 pieces, then spread with the avocado and top with radish, red onion and watercress. Serve at once.
Per serving: Calories 54 | Sugar 0.5g | Fat 3.4g | Saturates 0.6g | Salt 0.1g