Wash and dry 250 grams of seedless grapes (preferably a mix of red and green). Cut them into quarters and place them in a large mixing bowl.
Finely chop 1 small red onion, 1 green chili (deseeded for less heat), and a handful of fresh coriander leaves. Add them to the bowl with the grapes.
In a separate small bowl, whisk together the juice of 1 lime, 1 teaspoon of chaat masala, and 1/2 teaspoon of black salt. Pour this dressing over the grape mixture.
Gently toss the grape salsa to combine all the ingredients and ensure they are evenly coated with the dressing. Taste and adjust the seasoning if needed.
Cover the bowl and refrigerate the grape salsa for at least 30 minutes to allow the flavors to meld together. Serve chilled with tortilla chips or as a topping for grilled fish or chicken.