In a medium bowl, whisk together the oil, lemon juice, sugar, poppy seeds and salt. Set aside.
Half Brussels’ sprouts lengthwise, then slice thinly. Add to dressing.
Slice the apple into short matchsticks. Add to the dressing. Mix well.
Serve immediately or refrigerate for a few hours before enjoying.
If serving the salad after refrigerating, you will want to drain it before serving if it has released a lot of liquid. Remove any outer leaves of the Brussels sprouts that are bruised or have black spots on them before shaving for the salad.