Preheat oven to 375 degrees F (190 degrees C). Spray an 8-inch baking pan with cooking spray.
Combine water and amaranth in a small saucepan; bring to a boil. Reduce heat to medium-low and simmer until water is absorbed, about 15 minutes.
Mix peanut butter, applesauce, honey, and egg together in a bowl. Add cooked amaranth, garbanzo bean flour, oats, sunflower seeds, chia seeds, baking powder, and cinnamon and mix well; spread into prepared pan.
Bake in the preheated oven until edges are golden brown, about 20 minutes. Cut into wedges and store in a container in the refrigerator.
I bring the amaranth to a boil, then simmer for a few minutes, then turn off the heat. Later, if all water is not absorbed, I will turn on the heat again, and carefully watch to see when the bottom of the pan is almost dry! This is better made with a few drops of water that isn't absorbed than to chance letting the amaranth dry out!