Arrange chips in a single layer on platters. Mound potato, then onion, equally on chips.
Top each chip with about 1/2 teaspoon each spicy yogurt and tamarind-date chutney, 1/4 teaspoon green chutney, 1 teaspoon sev, and 1/4 teaspoon cilantro.
Spicy yogurt: In a bowl, mix 6 tablespoons plain nonfat yogurt, and 1/4 teaspoon each ground cumin, sugar, and salt. Makes about 6 tablespoons.
Green chutney: In a blender, combine 1 cup coarsely chopped fresh cilantro; 2 fresh jalapeño chilies (1 oz. total), rinsed, stemmed, and sliced; 1 tablespoon unsweetened shredded dried coconut; 1 tablespoon lime juice; and 1/2 teaspoon each sugar and salt. Whirl until smooth, adding just enough water (2 to 4 tablespoons) to facilitate blending. Cover and chill up to 1 day. Makes about 1/3 cup.