Mix the frozen yogurt and granola together in a medium bowl. Freeze until firm, at least 1 hour.
Preheat the oven to 400 degrees F. Spray a broiler-safe 8-inch square baking dish with cooking spray.
Peel and core the apples, then cut them in half vertically. Place the apple halves, cut-side-down, on a cutting board and make 1/8-inch-thick crosswise slices, stopping before you cut through to the bottom to keep the halves intact. Arrange the apples in the prepared baking dish.
Melt the butter and mix in the apple pie spice. Use half of the spiced butter to brush the apples and add to the bottom of the baking dish; reserve the other half for the crumb topping. Add 2 tablespoons water to the baking dish. Cover the baking dish with foil and bake for 30 minutes. Remove the foil and continue to bake until the apples are just tender and golden brown, about 30 minutes more.
Remove the dish from the oven and set aside until cool enough to handle, about 10 minutes. Preheat the broiler to high.
Meanwhile, mix the remaining spiced butter with the panko, pecans and sugar.
When the apples have cooled, gently separate each of the slices and spoon a small amount of the panko mixture in between. Sprinkle any remaining mixture on top.
Broil the apples until the topping is golden brown, about 2 minutes. Serve warm with the granola frozen yogurt.