Preheat oven to 375℉. In a large saucepan over medium-low heat, cook and stir zucchini and lemon juice until zucchini is tender, 15-20 minutes. Stir in sugar, cinnamon and nutmeg; cook 1 minute longer. Remove from the heat; set aside.
In a large bowl, combine flour and sugar; cut in butter until mixture resembles coarse crumbs. Stir ½ cup into zucchini mixture. Press half the remaining crust mixture into a greased 15x10x1” baking pan. Spread zucchini mixture over top; crumble remaining crust mixture over zucchini. Sprinkle with cinnamon.
Bake until golden and bubbly, 35-40 minutes. Cool in pan on a wire rack.