Toast the nuts in a dry pan or in the oven, then roughly chop them.

Cut the apples into cubes and immediately drizzle with lemon juice to prevent browning.

Slice the celery stalks thinly. If using grapes, cut them in half.

In a small bowl, mix the yogurt, mayonnaise, Dijon mustard, and the remaining lemon juice.

Transfer the apples, celery, grapes, and nuts into a large bowl. Add the dressing and gently mix until everything is evenly coated.

Serve immediately or chill for about 15 minutes — this makes the salad even more crisp and refreshing.