Preparation

1. Begin by preparing the walnut pumpkin seed brittle: Line a plate or baking sheet with parchment paper.
2. In a skillet over medium heat, melt the sugar until it becomes a light amber color, stirring gently.
3. Quickly stir in the walnuts, pumpkin seeds, and salt. Pour the mixture onto the prepared parchment and spread it out.
4. Let the brittle cool and break it into shards.
5. Prepare the yogurt dressing by whisking together Greek yogurt, a spoon of mayonnaise, lemon juice, honey, salt, black pepper, and cinnamon in a small bowl.
6. Chop the apples and toss them with a little lemon juice to prevent browning. Slice celery thinly and halve the grapes.

Assembly

1. In a large bowl, combine apples, celery, grapes, and chopped walnuts.
2. Fold in the yogurt dressing gently to avoid bruising the fruit.
3. Top with walnut pumpkin seed brittle just before serving.