Heat the oven to 350°F and parchment-line two light sheet pans.
Whisk oats, oat flour, flax, cinnamon, baking powder and salt.
Whisk banana, peanut butter, egg, maple syrup and vanilla until uniform.
Fold wet into dry, then fold in raisins until every oat is coated.
Rest 10 minutes. Add oat flour 1 tablespoon at a time if it smears or milk 1 teaspoon at a time if it crumbles.
Divide into 12 portions of about 72 grams, six per pan.
Press with damp fingertips into three-inch disks about one-half inch thick.
Bake 13 to 17 minutes, rotating around minute 8, until edges are light golden and centers matte and springy.
Cool on pans 10 minutes and on a rack at least 30 minutes before packing.
