Preheat oven to 400°.
. Lightly spoon flour into dry measuring cups; level with a knife. Combine flour and next 5 ingredients in a bowl. Cut in butter with a pastry blender or 2 knives until mixture resembles coarse meal. Stir in walnuts.
. Combine pumpkin and milk in a small bowl; stir well with a whisk. Add to flour mixture, stirring just until moist.
. Turn dough out onto a heavily floured surface; knead lightly 5 times with floured hands. Pat dough into a 9-inch square; cut dough into 16 square biscuits. Place biscuits on a baking sheet coated with cooking spray.
. Bake at 400° for 23 minutes or until lightly browned. Serve warm.