1 pound of ground chicken or boneless, skinless chicken breasts, finely minced (not pureed)
Salt and freshly ground pepper
Four 8-inch square spring roll wrappers
Put the whole cumin seeds in a small skillet and set over medium heat. Toast, shaking the pan occasionally, until fragrant and browned. The seeds will start to pop. Remove from the heat, cool completely, and grind to a fine powder in a spice grinder.
Place the cilantro leaves and chile in a food processor and process until coarsely chopped. Transfer to a mixing bowl and add the yogurt, lemon juice, sugar, and ½ teaspoon of the finely ground cumin. Stir well, season with salt, pepper, and more sugar to taste, and set aside.
Put the oil in a large deep skillet and set over medium heat. Add the onion and cook, stirring, until translucent and softened, about 5 minutes. Add the ginger and garlic and cook until fragrant, 1 minute, then add the coriander, turmeric, cayenne, and remaining ground cumin and cook, stirring, for 3 minutes. Add the tomatoes and cook until they begin to break down, 5 minutes, and stir in the tamarind paste. Add the chicken and cook, stirring, until the meat is completely cooked through, about 5 minutes. Season to taste with salt and pepper, remove from the heat, and cool to room temperature.
Put one of the spring roll wrapper rectangles on your work surface so that the short side is facing you. Put 2 tablespoons of the filling ¼ inch from the bottom of the rectangle, then fold the bottom left corner over the filling so that the bottom edge meets the right edge to form a triangle. Press the edges to seal, then fold the triangle over the top edge and continue to fold along the edges to create a triangle. Seal the end of the spring roll wrapper with a little water. Repeat with the remaining wrappers and filling.
Pour oil to a depth of 3 inches in a heavy, deep saucepan and heat to 350°F. Carefully add the samosas and cook, turning occasionally, until golden brown and crisp. Do not overcrowd; work in batches if necessary. Remove from the oil and drain on paper towels. Serve immediately with the cilantro-yogurt dip.