Preheat a small dry skillet over medium heat. Add walnuts and toast, stirring frequently, until fragrant and slightly darker, about 4–5 minutes. Remove from heat and transfer to a plate to stop cooking; roughly chop once cooled.

Prepare apples

Core and thinly slice the apples. To prevent browning, toss apple slices in a small bowl with 1 teaspoon lemon juice (from the dressing ingredient if using) or use immediately.

Assemble base

In a large salad bowl, combine the mixed salad greens, thinly sliced red onion, dried cranberries, and half of the toasted walnuts. Add the apple slices and gently toss to distribute ingredients evenly.

Add cheese (optional)

If using, sprinkle crumbled feta or goat cheese over the dressed salad just before serving.

Dressing

Make the dressing: In a small bowl or jar with a tight lid, combine apple cider vinegar, maple syrup (or honey), Dijon mustard, lemon juice (if using), salt, and pepper. Whisk or shake until salt dissolves. While whisking, slowly stream in the olive oil until the dressing emulsifies and becomes slightly thickened (or add all ingredients to jar and shake vigorously). Taste and adjust seasoning — add more maple syrup for sweetness or more vinegar for brightness.

Dress the salad: Right before serving, drizzle about 3–4 tablespoons of the dressing over the salad and toss gently to coat. Add more dressing as desired (reserve any extra dressing in the refrigerator for up to 5 days).

Finish and serve: Top the salad with the remaining toasted walnuts for crunch and a final sprinkle of black pepper. Serve immediately.