To prepare crust, combine cooked rice, 1/4 cup sugar, beaten egg whites and cinnamon.
Spray a 9-inch pie pan with non-stick vegetable spray.
Spread the rice mixture evenly over bottom and sides of pan, pressing lightly with fingertips or the back of a spoon to shape into a crust.
Bake at 350°F for 10 minutes; cool to room temperature.
For the filling, put the rhubarb in a saucepan with the zucchini, cherries, sugar, honey and 2 tablespoons orange juice and cinnamon; simmer over low heat for 15 to 20 minutes or until rhubarb and zucchini are tender; taste for tartness and add more honey or sugar as needed.
Place the remaining 3 tablespoons of orange juice in a bowl and sprinkle the gelatin powder over juice; let soak a few minutes to soften.
Turn the cooked rhubarb mixture into food processor (or use an immersion blender) and puree; return the pureed mixture to the saucepan and bring back to a simmer.
Pour gelatin into the hot puree and stir until the gelatin is completely dissolved, let cool to room temperature and then turn out into the crust.
Chill for several hours or overnight.