Preheat oven to 350°F. Grease an 8"×8" baking dish. Combine sugar with 1 1/2 tsp cinnamon. Place a layer of apple slices in bottom of pan and dust with sugar/cinnamon mixture. Continue layering apples and cinnamon/sugar until done. The apples should be almost to top of pan (they will cook down). For the topping, combine flour, brown sugar, 1/2 tsp cinnamon, nuts and oats in a large bowl; stir well. Work the butter into mixture with fingertips until evenly distributed. Place topping evenly over apples. Bake in the dish on a baking sheet on centre oven rack until topping is crunchy and apples are bubbling (55-60 minutes).