Toast the walnuts in a dry skillet over medium heat for 3-5 minutes, stirring frequently until fragrant and lightly golden, then set aside to cool (this step makes such a difference in flavor!).
Make the cranberry vinaigrette by combining fresh cranberries, apple cider vinegar, honey, and Dijon mustard in a blender or food processor.
Blend on high until the cranberries are completely pureed and the mixture is smooth, about 30 seconds.
With the blender running on low, slowly drizzle in the olive oil through the top opening until the dressing is emulsified and creamy.
Season the dressing with salt and pepper, then taste and adjust sweetness or tanginess to your preference (I sometimes add an extra drizzle of honey!).
In a large salad bowl, combine the mixed greens, dried cranberries, toasted walnuts, sliced apples, and red onion.
Drizzle about half of the cranberry vinaigrette over the salad and toss gently to coat all the ingredients evenly.
Top the salad with crumbled cheese and serve immediately with extra dressing on the side for anyone who wants more.