Preheat oven to 350ºF.
Place frozen fruit in an 8×8 baking dish. Add 2 Tablespoons of brown sugar, cornstarch, lemon juice, and optional ginger and/or flavor extract. Mix to combine.
In a medium bowl, whisk together oats, flour, remaining brown sugar, salt, and optional nuts and spices.
Cut butter into ½ inch cubes. Using your hands or a pastry cutter, work the butter into the dry ingredients until it makes a coarse crumbly mixture. Do not overmix. Sprinkle oat mixture on top of fruit in an even layer.
Bake for 40-45 minutes or until the topping is golden brown and the fruit mixture is bubbling around the edges of the pan. Cool slightly before serving. Enjoy!