Preheat oven to 375°F. Mix baking mix, 1 cup of the cereal, 2 Tbsp. of the brown sugar and the pumpkin pie spice in large bowl. Beat egg in medium bowl. Add pumpkin and milk; mix well. Add to cereal mixture; stir just until moistened.
Pour into greased 8-inch square baking pan. Mix remaining 1 cup cereal, remaining 4 Tbsp. brown sugar and butter until well blended. Sprinkle over batter.
Bake 35 minutes or until toothpick inserted in center comes out clean. Serve warm.