Wash and dry the grapes thoroughly. Halve them crosswise and place in a large bowl.
In a small bowl, whisk together the Greek yogurt, honey, lemon zest (if using), and a pinch of salt until smooth.
Pour the dressing over the grapes and gently fold until evenly coated.
Toast the sliced almonds in a dry skillet over medium heat for 2–3 minutes, stirring often, until golden and fragrant. Let cool completely.
Just before serving, sprinkle the toasted almonds and chopped pecans (if using) over the salad. Stir lightly.
Keep chilled in a cooler until ready to eat. Serve cold or at cool ambient temperature.