How to Make It
Preheat oven to 400°F. Heat 3 tablespoons oil in a large skillet over medium-high. Add onion, and cook, stirring often, until browned, 16 to 20 minutes. Add chiles, cumin seeds, peppercorns, cardamom, cinnamon, mustard seeds, and fenugreek seeds. Cook, stirring occasionally, until fragrant, about 1 minute and 30 seconds. Stir in tomato paste, vinegar, ginger, garlic, and sugar; cook, stirring constantly, until mixture begins to caramelize, about 3 minutes. Remove from heat. Process chile mixture, 1 3/4 cups water, and 1 teaspoon salt in a blender until mixture forms a smooth, thick sauce. Set aside.
Toss together sweet potato, ground black pepper, 1 teaspoon oil, and 1/4 teaspoon salt on a large rimmed baking sheet; spread in a single layer. Roast in preheated oven until just tender, about 12 minutes. Set aside.
Heat remaining 2 tablespoons oil in a large skillet over medium-high. Add corn kernels and bell pepper, and cook, stirring often, until vegetables begin to soften, 1 to 2 minutes. Stir in sweet potato, and cook 1 minute. Add 1 3/4 cups pureed chile sauce and remaining 1 teaspoon salt, and cook, stirring often, until just heated through, about 2 minutes.
To serve, open corn puff bags. Spoon 1/2 cup vegetable mixture over corn puffs in each bag. Top each with about 1/2 cup mango koochumbar, 1/2 ounce tamarind chutney, and 1/2 ounce queso fresco.