Thoroughly rinse the mixed greens and spin or pat them dry to ensure the dressing sticks well.
Cut the apple into thin slices just before mixing to keep them fresh and prevent browning, aiming for uniform thickness.
If you'd like, toast the walnuts briefly in a dry skillet over medium heat for around 3 to 4 minutes until they release a nutty aroma, stirring often.
In a small bowl, combine maple syrup, olive oil, apple cider vinegar, Dijon mustard, salt, and pepper, then whisk vigorously for about half a minute until the dressing is creamy and well blended.
Place the greens, apple slices, walnuts, cranberries, and feta cheese (if using) in a large salad bowl and gently toss to mix.
Pour roughly half of the dressing over the salad, tossing carefully to coat everything evenly; add more dressing according to your preference, saving any leftovers.
Serve the salad straight away to enjoy the best texture and freshness.