1. For the avocado dressing,combine all the ingredients except the milk in a processor and blend until smooth. Add a little milk or water if necessary to bring it to a thick but pourable consistency.
2. Heat a frying pan over medium heat,add the olive oil and fry the bacon until it's crisp. Remove with tongs,reserving the oil and bacon fat in the pan. For the tomato croutons,toss the sourdough in the passata and allow to stand for 10 minutes. Fry over medium heat in the reserved oil and bacon fat (adding more oil if necessary),for 4 to 5 minutes,until crisp. Allow to cool.
3. Place the lettuce wedges on a serving plate and pour the avocado dressing over the top to smother. Scatter with the bacon,onion and tomato croutons. Grind over plenty of black pepper and scatter with chives to serve.
Adam's tip: To keep lettuce wedges fresh,store in a large bowl of water in the fridge and drain or spin them well when ready to use. They'll keep perfectly crisp for about a week.