Combine the peaches, pineapple, the 2 tablespoons brown sugar, and tapioca in a medium bowl. Spoon into an 8x8x2-inch metal baking or foil pan; set aside.
Combine the oats, the 1/4 cup brown sugar, flour, cinnamon, and nutmeg in another bowl. Cut in butter or margarine until mixture resembles coarse crumbs; sprinkle over fruit mixture. Cover pan tightly with foil.
Grill about 50 minutes or until mixture is hot and bubbly. Serve warm, with ice cream, if desired. Makes 8 servings.