Place chocolate chips in a small, microwave-safe bowl. Heat in microwave for 1 minute, until melted. If not using a microwave, place chocolate chips in a heat-proof bowl over a pan of steaming water, and stir until melted. Stir in vegetable oil.
Put popcorn, marshmallows, and walnuts in a large bowl. Pour chocolate over mixture, tossing to coat.
Drop tablespoons full of the mixture onto a lined baking sheet.