Place zucchini and lemon juice in a large saucepan. Cover and cook over medium heat, stirring occasionally, until zucchini is tender, about 15 minutes. Add nutmeg, sugar and cinnamon; blend until sugar dissolves. Remove from the heat. Pour into a greased 13x9-in. baking pan.
For topping, combine brown sugar, flour, oats and butter until crumbly. Sprinkle over zucchini. Bake at 375° for 50 minutes or until topping is golden brown. Serve warm with whipped cream or ice cream if desired.