Preheat oven to 375°. In a large skillet, heat oil over medium-high heat; saute onion, garlic, ginger, cumin and jalapeno until onion is tender. Stir in seasonings until blended. Add mashed potatoes, peas and lemon juice; cook 4 minutes, stirring occasionally. Cool slightly. Stir in cheese, cashews and cilantro.
Unfold puff pastry. Cut each sheet into six rectangles; moisten edges lightly with water. Spoon about 2 tablespoons potato mixture down the center of each rectangle. Fold a long side over filling, fold short sides toward the center, then roll up. Press seams to seal. Place 2 in. apart on a greased baking sheet, seam side down.
Bake until golden brown, 18-22 minutes. Place remaining ingredients in a blender; cover and process until blended. Serve with pastries.