Preheat oven to 350 F and grease a baking sheet.
In a bowl, combine 1 cup canned pumpkin, 1 cup white sugar, 1/2 cup vegetable oil and 1 large egg. In a small bowl dissolve 1 teaspoon baking soda in 1 teaspoon milk and stir in the pumpkin mixture.
In a separate bowl, whisk together 2 cups all-purpose flour, 2 teaspoons baking powder, 2 teaspoons ground cinnamon and 1/2 teaspoon salt. Mix the flour mixture with the pumpkin mixture.
Stir in 2 cups semisweet chocolate chips, 1/2 cup chopped walnuts and 1 tablespoon vanilla extract.
Scoop spoonfuls of the mixture on the baking sheet and bake them for about 10 minutes until lightly brown.