Preheat the oven to 375 degrees F (190 degrees C). Lightly grease a 2-1/2 quart baking dish.

Place peaches in the prepared baking dish. Combine brown sugar, 3 tablespoons flour, lemon juice, lemon zest, and cinnamon; sprinkle over peaches.

Combine 1 cup flour, sugar, baking powder, salt, and nutmeg. Stir in egg and mix until mixture has pea-sized crumbles. Sprinkle mixture over peaches. Pour butter evenly over crumbles.

Bake in the preheated oven until the top is lightly browned, 37 to 40 minutes.