FILLING: Peel the zucchinis. Cut in half lengthwise, remove the seeds with a metal spoon, and chop into bite-size pieces.
In a large skillet, bring the zucchini, sugar, lemon juice, and cinnamon to a simmer over medium heat. Cook stirring occasionally for 10-15 minutes until tender-crisp and sweet (do not overcook or you will have mush). Transfer the zucchini with the liquid to a 2 1/2-quart casserole dish.
CRUMB TOPPING: In a large bowl, stir together the flour, brown sugar, oats, cinnamon, and salt. Add the cubes of cold butter to the flour mixture. Use your hands to blend the mixture until the butter is evenly distributed and the topping is crumbly.
Sprinkle the crumble over the zucchini squeezing some of the crumbs in your hands for bigger crumbs.
Bake for 25-30 minutes or until the juices are bubbling and the top is golden brown. Place the crisp on a wire rack to cool completely.
Serve with a big scoop of vanilla ice cream. Enjoy!