In a saucepan, bring water to a boil. Add zucchini; cook for 3 minutes. Drain and pat dry. In a bowl, combine the zucchini, sugars, flour, lemon juice, cinnamon, cream of tartar and salt. Transfer to a greased 1-1/2-qt. baking dish.
For topping, in a bowl, combine the flour and sugars. Cut in butter until mixture resembles coarse crumbs. Sprinkle over zucchini mixture.
Bake at 375° for 45-50 minutes or until topping is golden brown and filling is bubbly around the edges.