Preheat the oven to 375 degrees F (190 degrees C).

Combine oats, granola, brown sugar, and 3 tablespoons flour in a medium bowl. Cut in 1/4 cup butter until crumbly.

Place peach slices into an 8-inch square baking dish. Sprinkle with remaining 1 tablespoon flour. Scatter oat mixture over peaches, then sprinkle with cinnamon, nutmeg, and allspice, followed by pecans.

Bake in the preheated oven until golden brown, about 30 minutes.