Roughly chop the salad leaves and place in a large bowl.
Core and slice the apple, finely chop the onion, slice the cranberries, crumble the goat's cheese and break the walnuts into small pieces.
Add all ingredients to the salad leaves and mix.
To make the salad dressing, squeeze the half lemon into a bowl, add the mustard and olive oil and stir. Pour over the salad and enjoy!