Combine first 10 ingredients in a large bowl; stir well. Place in a lightly greased 11" x 7" baking dish.
Combine flour and 1/4 cup brown sugar. Cut in 3 Tbsp. butter with a pastry blender until crumbly. Stir in nuts. Sprinkle over squash. Bake, uncovered, at 375° for 40 minutes or until edges are lightly browned. Let casserole stand 5 minutes before serving.