Preheat the oven to 350 degrees F (175 degrees C).
Grind 2 1/2 cups oats and hemp together in a food processor. Transfer to a large bowl. Add 3 cups flour, brown sugar, salt, cinnamon, baking soda, and allspice. Rub in butter and coconut oil by hand until mixture forms crumbs the size of frozen peas.
Add water to the bowl with the oat mixture. Knead until dough is uniform and moist, adding a small amount of additional water if necessary.
Turn dough out onto a surface dusted with 1 tablespoon flour and 1 tablespoon oats. Pat down to about 1 1/2-inch thickness. Cut cakes into desired shapes and place on a baking sheet.
Bake in the preheated oven until cakes are dry and firm, 16 to 20 minutes.