Place 3/4 of the apple slices in two quart baking dish, covering the bottom of the dish. Sprinkle with lemon juice. Combine flour, sugar, oats, cinnamon, and nutmeg. Cut butter into one-inch chunks. Blend into dry ingredients, using a pastry blender or two forks. When crumbly, sprinkle 1/4 of mixture over apples. Place the remaining apples in the dish. Sprinkle remaining mixture over apples. Bake at 375 degrees for 15 minutes. Turn oven down to 350 degrees and bake for 30 minutes more.