Rinse the mixed greens and dry thoroughly using a salad spinner or clean towels to ensure dressing sticks properly.
Cut the apple into thin slices right before adding to the salad to avoid browning and maintain freshness.
Toast the walnuts lightly in a dry skillet over medium heat for 3 to 4 minutes until they release a nice aroma, stirring often to prevent burning.
Combine maple syrup, olive oil, apple cider vinegar, Dijon mustard, salt, and pepper in a small bowl and whisk briskly for about 30 seconds until the dressing is creamy and well blended.
In a big bowl, carefully mix the greens, apple slices, toasted walnuts, dried cranberries, and feta cheese if using.
Pour about half of the dressing over the salad and toss gently to coat everything evenly, adding more dressing to your liking.
Serve the salad right away for the best flavor and texture.