Preheat the oven to 350 degrees F (175 degrees C).
In a medium bowl, mix together the cantaloupe, lemon juice, sugar, flour, 2 tablespoons melted butter, cinnamon, nutmeg and vanilla. Transfer to a 9 inch square baking dish, and spread the dry cake mix evenly over the top. Drizzle the remaining melted butter over the cake mix.
Bake for 45 minutes in the preheated oven, or until the top is golden brown.