In a bowl combine apple slices, granulated sugar, cinnamon & orange juice. Mix lightly & place in a greased 2 quart casserole. Sift flour & baking powder together. Cut in the margarine & rub with fingertips to a crumbly consistency. Combine brown sugar & egg. Add to flour mixture along with nuts. Sprinkle over apples. Bake in 350 oven for 45 minutes, or until apples are tender & crust is golden brown.