Heat oil in a non stick kadai. Add cumin seeds and sauté till fragrant. Halve the grapes and remove the seeds. Add walnuts to the kadai and sauté. Add grapes, red chilli powder, roasted cumin powder, salt and sauté.
Add salt to yogurt and mix. Keeping aside a little walnut-grape mixture, transfer the rest into a serving bowl. Add the yogurt and mix well.Top it with the remaining walnut-grape mixture. Drizzle Rooh afza and serve.